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Sample records for ir heavy fermion

  1. Vortexlike excitations in the heavy-fermion superconductor CeIrIn5

    DOE PAGES

    Luo, Yongkang; Rosa, P. F. S.; Bauer, E. D.; ...

    2016-05-05

    Here, we report a systematic study of temperature- and field-dependent charge (ρ) and entropy (S) transport in the heavy-fermion superconductor CeIrIn5. Its large positive thermopower Sxx is typical of Ce-based Kondo lattice systems, and strong electronic correlations play an important role in enhancing the Nernst signal Sxy. By separating the off-diagonal Peltier coefficient αxy from Sxy, we find that αxy becomes positive and greatly enhanced at temperatures well above the bulk Tc. Compared with the nonmagnetic analog LaIrIn5, these results suggest vortexlike excitations in a precursor state to unconventional superconductivity in CeIrIn5. This study sheds light on the similarity ofmore » heavy-fermion and cuprate superconductors and on the possibility of states not characterized by the amplitude of an order parameter.« less

  2. Vortexlike excitations in the heavy-fermion superconductor CeIrIn5

    NASA Astrophysics Data System (ADS)

    Luo, Yongkang; Rosa, P. F. S.; Bauer, E. D.; Thompson, J. D.

    2016-05-01

    We report a systematic study of temperature- and field-dependent charge (ρ ) and entropy (S ) transport in the heavy-fermion superconductor CeIrIn5. Its large positive thermopower Sx x is typical of Ce-based Kondo lattice systems, and strong electronic correlations play an important role in enhancing the Nernst signal Sx y. By separating the off-diagonal Peltier coefficient αx y from Sx y, we find that αx y becomes positive and greatly enhanced at temperatures well above the bulk Tc. Compared with the nonmagnetic analog LaIrIn5, these results suggest vortexlike excitations in a precursor state to unconventional superconductivity in CeIrIn5. This study sheds light on the similarity of heavy-fermion and cuprate superconductors and on the possibility of states not characterized by the amplitude of an order parameter.

  3. Heavy fermion quantum criticality.

    PubMed

    Nazario, Zaira; Santiago, David I

    2008-09-26

    During the last few years, investigations of rare-earth materials have made clear that heavy fermion quantum criticality exhibits novel physics not fully understood. In this work, we write for the first time the effective action describing the low energy physics of the system. The f fermions are replaced by a dynamical scalar field whose nonzero expected value corresponds to the heavy fermion phase. The effective theory is amenable to numerical studies as it is bosonic, circumventing the fermion sign problem. Via effective action techniques, renormalization group studies, and Callan-Symanzik resummations, we describe the heavy fermion criticality and predict the heavy fermion critical dynamical susceptibility and critical specific heat. The specific heat coefficient exponent we obtain (0.39) is in excellent agreement with the experimental result at low temperatures (0.4).

  4. Unique spin dynamics and unconventional superconductivity in the layered heavy fermion compound CeIrIn5: NQR evidence.

    PubMed

    Zheng, G; Tanabe, K; Mito, T; Kawasaki, S; Kitaoka, Y; Aoki, D; Haga, Y; Onuki, Y

    2001-05-14

    We report measurements of the 115In nuclear spin-lattice relaxation rate ( 1/T1) between T = 0.09 and 100 K in the new heavy fermion (HF) compound CeIrIn5. At 0.4 < or = T< or = 100 K, 1/T1 is strongly T-dependent, which indicates that CeIrIn5 is much more itinerant than known Ce-based HFs. We find that 1/T1T, subtracting that for LaIrIn5, follows a (1 / T+straight theta)3/4 variation with straight theta = 8 K. We argue that this novel feature points to anisotropic, due to a layered crystal structure, spin fluctuations near a magnetic ordering. The bulk superconductivity sets in at 0.40 K below which the coherence peak is absent and 1/T1 follows a T3 variation, which suggests unconventional superconductivity with line-node gap.

  5. Physical properties of the Ce2MAl7Ge4 heavy-fermion compounds (M=Co,Ir,Ni,Pd)

    DOE PAGES

    Ghimire, N. J.; Cary, S. K.; Eley, S.; ...

    2016-05-23

    Here, we report the synthesis, crystal structure, and characterization by means of single-crystal x-ray diffraction, neutron powder diffraction, and magnetic, thermal, and transport measurements of the new heavy-fermion compounds Ce2MAl7Ge4 (M=Co,Ir,Ni,Pd). These compounds crystallize in a noncentrosymmetric tetragonal space group Pmore » $$\\bar{4}$$21m, consisting of layers of square nets of Ce atoms separated by Ge-Al and M-Al-Ge blocks. Ce2CoAl7Ge4,Ce2IrAl7Ge4, and Ce2NiAl7Ge4 order magnetically below TM=1.8, 1.6, and 0.8 K, respectively. There is no evidence of magnetic ordering in Ce2PdAl7Ge4 down to 0.4 K. Furthermore, the small amount of entropy released in the magnetic state of Ce2MAl7Ge4 (M = Co, Ir, Ni) and the reduced specific heat jump at TM suggest a strong Kondo interaction in these materials. Ce2PdAl7Ge4 shows non-Fermi liquid behavior, possibly due to the presence of a nearby quantum critical point.« less

  6. Signatures of spin-glass behaviour in PrIr2B2 and heavy fermion behaviour in PrIr2B2C.

    PubMed

    Anupam; Anand, V K; Hossain, Z; Adroja, D T; Geibel, C

    2011-09-21

    CEF-split singlet and the first excited state singlet is situated 15 K above the ground state. The Sommerfeld coefficient γ∼300 mJ mol(-1) K(-2) of PrIr(2)B(2)C is very high and reflects a heavy fermion behaviour in this compound. We believe that the heavy fermion state in PrIr(2)B(2)C has its origin in low lying crystal field excitations as has been observed in PrRh(2)B(2)C.

  7. Heavy fermion superconductivity

    NASA Astrophysics Data System (ADS)

    Brison, Jean-Pascal; Glémot, Loı̈c; Suderow, Hermann; Huxley, Andrew; Kambe, Shinsaku; Flouquet, Jacques

    2000-05-01

    The quest for a precise identification of the symmetry of the order parameter in heavy fermion systems has really started with the discovery of the complex superconducting phase diagram in UPt 3. About 10 years latter, despite numerous experiments and theoretical efforts, this is still not achieved, and we will quickly review the present status of knowledge and the main open question. Actually, the more forsaken issue of the nature of the pairing mechanism has been recently tackled by different groups with macroscopic or microscopic measurement, and significant progress have been obtained. We will discuss the results emerging from these recent studies which all support non-phonon-mediated mechanisms.

  8. Vortexlike excitations in the heavy-fermion superconductor CeIrIn5

    SciTech Connect

    Luo, Yongkang; Rosa, P. F. S.; Bauer, E. D.; Thompson, J. D.

    2016-05-05

    Here, we report a systematic study of temperature- and field-dependent charge (ρ) and entropy (S) transport in the heavy-fermion superconductor CeIrIn5. Its large positive thermopower Sxx is typical of Ce-based Kondo lattice systems, and strong electronic correlations play an important role in enhancing the Nernst signal Sxy. By separating the off-diagonal Peltier coefficient αxy from Sxy, we find that αxy becomes positive and greatly enhanced at temperatures well above the bulk Tc. Compared with the nonmagnetic analog LaIrIn5, these results suggest vortexlike excitations in a precursor state to unconventional superconductivity in CeIrIn5. This study sheds light on the similarity of heavy-fermion and cuprate superconductors and on the possibility of states not characterized by the amplitude of an order parameter.

  9. Vortexlike excitations in the heavy-fermion superconductor CeIrIn5

    SciTech Connect

    Luo, Yongkang; Rosa, P. F. S.; Bauer, E. D.; Thompson, J. D.

    2016-05-05

    Here, we report a systematic study of temperature- and field-dependent charge (ρ) and entropy (S) transport in the heavy-fermion superconductor CeIrIn5. Its large positive thermopower Sxx is typical of Ce-based Kondo lattice systems, and strong electronic correlations play an important role in enhancing the Nernst signal Sxy. By separating the off-diagonal Peltier coefficient αxy from Sxy, we find that αxy becomes positive and greatly enhanced at temperatures well above the bulk Tc. Compared with the nonmagnetic analog LaIrIn5, these results suggest vortexlike excitations in a precursor state to unconventional superconductivity in CeIrIn5. This study sheds light on the similarity of heavy-fermion and cuprate superconductors and on the possibility of states not characterized by the amplitude of an order parameter.

  10. Intermediate valence to heavy fermion through a quantum phase transition in Yb3(Rh1-xTx)4Ge13 (T = Co, Ir) single crystals

    NASA Astrophysics Data System (ADS)

    Rai, Binod; Morosan, Emilia

    Single crystals of Yb3(Rh1-x Tx)4Ge13 (T = Co, Ir) have been grown using the self-flux method. Powder X-ray diffraction data on these compounds are consistent with the cubic structure with space group Pm 3 n . Intermediate valence behavior is observed in Yb3(Rh1-x Tx)4Ge13 upon T = Co doping, while T = Ir doping drives the system into a heavy fermion state. Antiferromagnetic order is observed in the Ir-doped samples Yb3(Rh1-x Tx)4Ge13 for 0.5 < x <= 1 with TN = 0.96 K for Yb3Ir4Ge13. With decreasing x, the magnetic order is suppressed towards a quantum critical point around xc = 0.5, accompanied by non-Fermi liquid behavior evidenced by logarithmic divergence of the specific heat and linear temperature dependence of the resistivity. The Fermi liquid behavior is recovered with the application of large magnetic fields. Gordon and Betty Moore Foundation EPiQS initiative through Grant GBMF4417 and Welch Foundation.

  11. Spin susceptibility of noncentrosymmetric heavy-fermion superconductor CeIrSi3 under pressure: 29Si Knight-shift study on single crystal.

    PubMed

    Mukuda, H; Ohara, T; Yashima, M; Kitaoka, Y; Settai, R; Onuki, Y; Itoh, K M; Haller, E E

    2010-01-08

    We report 29Si NMR study on a single crystal of the heavy-fermion superconductor CeIrSi3 without an inversion symmetry along the c axis. The 29Si Knight-shift measurements under pressure have revealed that the spin susceptibility for the ab plane decreases slightly below T(c), whereas along the c axis it does not change at all. The result can be accounted for by the spin susceptibility in the superconducting state being dominated by the strong antisymmetric (Rashba-type) spin-orbit interaction that originates from the absence of an inversion center along the c axis and it being much larger than superconducting condensation energy. This is the first observation which exhibits an anisotropy of the spin susceptibility below T(c) in the noncentrosymmetric superconductor dominated by strong Rashba-type spin-orbit interaction.

  12. Spin Susceptibility of Noncentrosymmetric Heavy-Fermion Superconductor CeIrSi3 under Pressure: Si29 Knight-Shift Study on Single Crystal

    NASA Astrophysics Data System (ADS)

    Mukuda, H.; Ohara, T.; Yashima, M.; Kitaoka, Y.; Settai, R.; Ōnuki, Y.; Itoh, K. M.; Haller, E. E.

    2010-01-01

    We report Si29 NMR study on a single crystal of the heavy-fermion superconductor CeIrSi3 without an inversion symmetry along the c axis. The Si29 Knight-shift measurements under pressure have revealed that the spin susceptibility for the ab plane decreases slightly below Tc, whereas along the c axis it does not change at all. The result can be accounted for by the spin susceptibility in the superconducting state being dominated by the strong antisymmetric (Rashba-type) spin-orbit interaction that originates from the absence of an inversion center along the c axis and it being much larger than superconducting condensation energy. This is the first observation which exhibits an anisotropy of the spin susceptibility below Tc in the noncentrosymmetric superconductor dominated by strong Rashba-type spin-orbit interaction.

  13. Physical properties of the Ce2M Al 7Ge4 heavy-fermion compounds (M =Co,Ir,Ni,Pd)

    NASA Astrophysics Data System (ADS)

    Ghimire, N. J.; Cary, S. K.; Eley, S.; Wakeham, N. A.; Rosa, P. F. S.; Albrecht-Schmitt, T.; Lee, Y.; Janoschek, M.; Brown, C. M.; Civale, L.; Thompson, J. D.; Ronning, F.; Bauer, E. D.

    2016-05-01

    We report the synthesis, crystal structure, and characterization by means of single-crystal x-ray diffraction, neutron powder diffraction, and magnetic, thermal, and transport measurements of the new heavy-fermion compounds Ce2MAl 7Ge4 (M =Co,Ir,Ni,Pd). These compounds crystallize in a noncentrosymmetric tetragonal space group P 4 ¯21m , consisting of layers of square nets of Ce atoms separated by Ge-Al and M-Al-Ge blocks. Ce2CoAl7Ge4,Ce2IrAl7Ge4 , and Ce2NiAl7Ge4 order magnetically below TM= 1.8 , 1.6, and 0.8 K, respectively. There is no evidence of magnetic ordering in Ce2PdAl7Ge4 down to 0.4 K. The small amount of entropy released in the magnetic state of Ce2M Al7Ge4 (M = Co, Ir, Ni) and the reduced specific heat jump at TM suggest a strong Kondo interaction in these materials. Ce2PdAl7Ge4 shows non-Fermi liquid behavior, possibly due to the presence of a nearby quantum critical point.

  14. NMR and NQR studies of the heavy fermion superconductors CeTIn{sub 5} (T=Co and Ir)

    SciTech Connect

    Kohori, Y.; Yamato, Y.; Iwamoto, Y.; Kohara, T.; Bauer, E. D.; Maple, M. B.; Sarrao, J. L.

    2001-10-01

    We have carried out {sup 115}In and {sup 59}Co nuclear quadrupole resonance and nuclear magnetic resonance measurements on CeCoIn{sub 5} and CeIrIn{sub 5}. The temperature T dependence of the nuclear spin-lattice relaxation rate 1/T{sub 1} of {sup 115}In in the normal state indicates that CeCoIn{sub 5} is located just at an antiferromagnetic instability, and CeIrIn{sub 5} is in the nearly antiferromagnetic region. In the superconducting state, 1/T{sub 1} has no Hebel-Slichter coherence peak just below T{sub C} and a power-law T dependence (close to T{sup 3}) at very low temperatures, which indicates the existence of line nodes in the superconducting energy gap. The {sup 115}In (Ce-In plane) Knight shift in CeCoIn{sub 5} decreases for both parallel and perpendicular directions to the tetragonal c axis in the superconducting state, which shows that the spin susceptibility decreases in all directions. These results indicate that CeCoIn{sub 5} and CeIrIn{sub 5} exhibit non-s-wave even parity (probably d-wave) superconductivity.

  15. Enhancement of Superconducting Transition Temperature due to the Strong Antiferromagnetic Spin Fluctuations in the Noncentrosymmetric Heavy-Fermion Superconductor CeIrSi3: A Si29 NMR Study under Pressure

    NASA Astrophysics Data System (ADS)

    Mukuda, H.; Fujii, T.; Ohara, T.; Harada, A.; Yashima, M.; Kitaoka, Y.; Okuda, Y.; Settai, R.; Onuki, Y.

    2008-03-01

    We report a Si29 NMR study on the pressure-induced superconductivity (SC) in an antiferromagnetic (AFM) heavy-fermion compound CeIrSi3 without inversion symmetry. In the SC state at P=2.7 2.8GPa, the temperature (T) dependence of the nuclear-spin lattice relaxation rate 1/T1 below Tc exhibits a T3 behavior without any coherence peak just below Tc, revealing the presence of line nodes in the SC gap. In the normal state, 1/T1 follows a T-like behavior, suggesting that the SC emerges under the non-Fermi-liquid state dominated by AFM spin fluctuations enhanced around a quantum critical point. The reason why the maximum Tc in CeIrSi3 is relatively high among the Ce-based heavy-fermion superconductors may be the existence of the strong AFM spin fluctuations. We discuss the comparison with the other Ce-based heavy-fermion superconductors.

  16. Enhancement of superconducting transition temperature due to the strong antiferromagnetic spin fluctuations in the noncentrosymmetric heavy-fermion superconductor CeIrSi3: A 29Si NMR study under pressure.

    PubMed

    Mukuda, H; Fujii, T; Ohara, T; Harada, A; Yashima, M; Kitaoka, Y; Okuda, Y; Settai, R; Onuki, Y

    2008-03-14

    We report a (29)Si NMR study on the pressure-induced superconductivity (SC) in an antiferromagnetic (AFM) heavy-fermion compound CeIrSi(3) without inversion symmetry. In the SC state at P = 2.7-2.8 GPa, the temperature (T) dependence of the nuclear-spin lattice relaxation rate 1/T(1) below T(c) exhibits a T(3) behavior without any coherence peak just below T(c), revealing the presence of line nodes in the SC gap. In the normal state, 1/T(1) follows a square root T-like behavior, suggesting that the SC emerges under the non-Fermi-liquid state dominated by AFM spin fluctuations enhanced around a quantum critical point. The reason why the maximum T(c) in CeIrSi(3) is relatively high among the Ce-based heavy-fermion superconductors may be the existence of the strong AFM spin fluctuations. We discuss the comparison with the other Ce-based heavy-fermion superconductors.

  17. Electric field gradients of CeMIn5 (M= Co, Rh, Ir) heavy-fermion systems studied by perturbed angular correlations and ab initio electronic structure calculations

    NASA Astrophysics Data System (ADS)

    Forker, M.; Silva, P. R. J.; Cavalcante, J. T. P. D.; Cavalcante, F. H. M.; Ramos, S. M.; Saitovitch, H.; Baggio-Saitovitch, E.; Alonso, R.; Taylor, M.; Errico, L. A.

    2013-04-01

    The electric field gradient (EFG) at the highly dilute nuclear probe 111Cd in the heavy fermion systems CeMIn5, M= Co, Rh, and Ir and YCoIn5 has been investigated by perturbed angular correlation (PAC) measurements of the nuclear electric quadrupole interaction (QI) of 111Cd on In sites. Pure and Sn-doped single crystals prepared by In-flux synthesis and polycrystalline samples prepared by arc melting have been studied. The samples were doped with the PAC probe 111Cd by diffusion of the mother isotope 111In. In all samples, several fractions of 111Cd probe nuclei subject to different QI's have been observed, among them a large fraction of 111Cd in unreacted In metal. Detailed calculations of the EFG at In nuclei and at Cd probes on In sites of pure and Sn-doped CeMIn5 were preformed, using the full-potential augmented plane wave+local orbital (APW+lo) formalism and taking into account different variables such as the electronic structure of the hyperfine probes, probe induced structural distortions, and impurity doping. The excellent agreement between the predicted EFG's and the experimental results allows us to assign two of the observed EFG components to the lattice sites 1c and 4i of the CeMIn5 compounds and to explain the pronounced difference of the EFG at In and Cd probes on the same lattice position. Structural distortions induced by the Cd probe and Sn-doping were found to have little effect on the EFG at the Cd probes. We also show that the local spin density approximation (LSDA) and LDA+U calculations predict very similar equilibrium structures and EFG's at the In/Cd sites. The extension of the experiments and the calculations from CeMIn5 to YCoIn5 and LaCoIn5 have established that the influence of the 4f electrons on the EFG's at impurity sites is negligibly small.

  18. Superfluid response in heavy fermion superconductors

    NASA Astrophysics Data System (ADS)

    Zhong, Yin; Zhang, Lan; Shao, Can; Luo, Hong-Gang

    2017-10-01

    Motivated by a recent London penetration depth measurement [H. Kim, et al., Phys. Rev. Lett. 114, 027003 (2015)] and novel composite pairing scenario [O. Erten, R. Flint, and P. Coleman, Phys. Rev. Lett. 114, 027002 (2015)] of the Yb-doped heavy fermion superconductor CeCoIn5, we revisit the issue of superfluid response in the microscopic heavy fermion lattice model. However, from the literature, an explicit expression for the superfluid response function in heavy fermion superconductors is rare. In this paper, we investigate the superfluid density response function in the celebrated Kondo-Heisenberg model. To be specific, we derive the corresponding formalism from an effective fermionic large- N mean-field pairing Hamiltonian whose pairing interaction is assumed to originate from the effective local antiferromagnetic exchange interaction. Interestingly, we find that the physically correct, temperature-dependent superfluid density formula can only be obtained if the external electromagnetic field is directly coupled to the heavy fermion quasi-particle rather than the bare conduction electron or local moment. Such a unique feature emphasizes the key role of the Kondo-screening-renormalized heavy quasi-particle for low-temperature/energy thermodynamics and transport behaviors. As an important application, the theoretical result is compared to an experimental measurement in heavy fermion superconductors CeCoIn5 and Yb-doped Ce1- x Yb x CoIn5 with fairly good agreement and the transition of the pairing symmetry in the latter material is explained as a simple doping effect. In addition, the requisite formalism for the commonly encountered nonmagnetic impurity and non-local electrodynamic effect are developed. Inspired by the success in explaining classic 115-series heavy fermion superconductors, we expect the present theory will be applied to understand other heavy fermion superconductors such as CeCu2Si2 and more generic multi-band superconductors.

  19. The physics and chemistry of heavy fermions.

    PubMed Central

    Fisk, Z; Sarrao, J L; Smith, J L; Thompson, J D

    1995-01-01

    The heavy fermions are a subset of the f-electron intermetallic compounds straddling the magnetic/nonmagnetic boundary. Their low-temperature properties are characterized by an electronic energy scale of order 1-10 K. Among the low-temperature ground states observed in heavy fermion compounds are exotic superconductors and magnets, as well as unusual semiconductors. We review here the current experimental and theoretical understanding of these systems. PMID:11607558

  20. Plutonium-Based Heavy-Fermion Systems

    NASA Astrophysics Data System (ADS)

    Bauer, E. D.; Thompson, J. D.

    2015-03-01

    An effective mass of charge carriers that is significantly larger than the mass of a free electron develops at low temperatures in certain lanthanide- and actinide-based metals, including those formed with plutonium, owing to strong electron-electron interactions. This heavy-fermion mass is reflected in a substantially enhanced electronic coefficient of specific heat γ, which for elemental Pu is much larger than that of normal metals. By our definition, there are twelve Pu-based heavy-fermion compounds, most discovered recently, whose basic properties are known and discussed. Relative to other examples, these Pu-based heavy-fermion systems are particularly complex owing in part to the possible simultaneous presence of multiple, nearly degenerate 5fn configurations. This complexity poses significant opportunities as well as challenges, including understanding the origin of unconventional superconductivity in some of these materials.

  1. Heavy fermion behavior explained by bosons

    NASA Technical Reports Server (NTRS)

    Kallio, A.; Poykko, S.; Apaja, V.

    1995-01-01

    Conventional heavy fermion (HF) theories require existence of massive fermions. We show that heavy fermion phenomena can also be simply explained by existence of bosons with moderate mass but temperature dependent concentration below the formation temperature T(sub B), which in turn is close to room temperature. The bosons B(++) are proposed to be in chemical equilibrium with a system of holes h(+): B(++) = h(+) + h(+). This equilibrium is governed by a boson breaking function f(T), which determines the decreasing boson density and the increasing fermion density with increasing temperature. Since HF-compounds are hybridized from minimum two elements, we assume in addition existence of another fermion component h(sub s)(+) with temperature independent density. This spectator component is thought to be the main agent in binding the bosons in analogy with electronic or muonic molecules. Using a linear boson breaking function we can explain temperature dependence of the giant linear specific heat coefficient gamma(T) coming essentially from bosons. The maxima in resistivity, Hall coefficient, and susceptibility are explained by boson localization effects due to the Wigner crystallization. The antiferromagnetic transitions in turn are explained by similar localization of the pairing fermion system when their density n(sub h)(T(sub FL)) becomes lower than n(sub WC), the critical density of Wigner crystallization. The model applies irrespective whether a compound is superconducting or not. The same model explains the occurrence of low temperature antiferromagnetism also in high-T(sub c) superconductors. The double transition in UPt3 is proposed to be due to the transition of the pairing fermion liquid from spin polarized to unpolarized state.

  2. Magnetism and superconductivity of heavy fermion matter

    NASA Astrophysics Data System (ADS)

    Flouquet, Jacques; Knebel, Georg; Braithwaite, Daniel; Aoki, D.; Brison, Jean-Pascal; Hardy, Frédéric; Huxley, Andrew; Raymond, Stéphane; Salce, Bernard; Sheikin, Ilya

    2006-01-01

    The interplay of magnetism and unconventional superconductivity (d singlet wave or p triplet wave) in a strongly correlated electronic system (SCES) is discussed with recent examples found in heavy fermion compounds. A short presentation is given on the formation of the heavy quasiparticle with the two sources of a local and intersite enhancement for the effective mass. Two cases of the coexistence or repulsion of antiferromagnetism and superconductivity are given with CeIn 3 and CeCoIn 5. A spectacular example is the emergence of superconductivity in relatively strong itinerant ferromagnets UGe 2 and URhGe. The impact of heavy fermion matter among other SCES as organic conductor or high T oxide is briefly pointed out. To cite this article: J. Flouquet et al., C. R. Physique 7 (2006).

  3. Unconventional superconductivity in heavy-fermion compounds

    SciTech Connect

    White, B. D.; Thompson, J. D.; Maple, M. B.

    2015-02-27

    Over the past 35 years, research on unconventional superconductivity in heavy-fermion systems has evolved from the surprising observations of unprecedented superconducting properties in compounds that convention dictated should not superconduct at all to performing explorations of rich phase spaces in which the delicate interplay between competing ground states appears to support emergent superconducting states. In this article, we review the current understanding of superconductivity in heavy-fermion com- pounds and identify a set of characteristics that is common to their unconventional superconducting states. These core properties are compared with those of other classes of unconventional superconductors such as the cuprates and iron-based superconductors. Lastly, we conclude by speculating on the prospects for future research in this field and how new advances might contribute towards resolving the long-standing mystery of how unconventional superconductivity works.

  4. Unconventional superconductivity in heavy-fermion compounds

    DOE PAGES

    White, B. D.; Thompson, J. D.; Maple, M. B.

    2015-02-27

    Over the past 35 years, research on unconventional superconductivity in heavy-fermion systems has evolved from the surprising observations of unprecedented superconducting properties in compounds that convention dictated should not superconduct at all to performing explorations of rich phase spaces in which the delicate interplay between competing ground states appears to support emergent superconducting states. In this article, we review the current understanding of superconductivity in heavy-fermion com- pounds and identify a set of characteristics that is common to their unconventional superconducting states. These core properties are compared with those of other classes of unconventional superconductors such as the cuprates andmore » iron-based superconductors. Lastly, we conclude by speculating on the prospects for future research in this field and how new advances might contribute towards resolving the long-standing mystery of how unconventional superconductivity works.« less

  5. Unconventional superconductivity in heavy-fermion compounds

    NASA Astrophysics Data System (ADS)

    White, B. D.; Thompson, J. D.; Maple, M. B.

    2015-07-01

    Over the past 35 years, research on unconventional superconductivity in heavy-fermion systems has evolved from the surprising observations of unprecedented superconducting properties in compounds that convention dictated should not superconduct at all to performing explorations of rich phase spaces in which the delicate interplay between competing ground states appears to support emergent superconducting states. In this article, we review the current understanding of superconductivity in heavy-fermion compounds and identify a set of characteristics that is common to their unconventional superconducting states. These core properties are compared with those of other classes of unconventional superconductors such as the cuprates and iron-based superconductors. We conclude by speculating on the prospects for future research in this field and how new advances might contribute towards resolving the long-standing mystery of how unconventional superconductivity works.

  6. Magnetoresistance in paramagnetic heavy fermion metals.

    PubMed

    Parihari, D; Vidhyadhiraja, N S

    2009-10-07

    A theoretical study of magnetic field (h) effects on single-particle spectra and the transport quantities of heavy fermion metals in the paramagnetic phase is carried out. We have employed a non-perturbative local moment approach (LMA) to the asymmetric periodic Anderson model within the dynamical mean field framework. The lattice coherence scale ω(L), which is proportional within the LMA to the spin-flip energy scale, and has been shown in earlier studies to be the energy scale at which crossover to single-impurity physics occurs, increases monotonically with increasing magnetic field. The many body Kondo resonance in the density of states at the Fermi level splits into two, with the splitting being proportional to the field itself. For h≥0, we demonstrate adiabatic continuity from the strongly interacting case to a corresponding non-interacting limit, thus establishing Fermi liquid behaviour for heavy fermion metals in the presence of a magnetic field. In the Kondo lattice regime, the theoretically computed magnetoresistance is found to be negative in the entire temperature range. We argue that such a result could be understood at [Formula: see text] by field-induced suppression of spin-flip scattering and at [Formula: see text] through lattice coherence. The coherence peak in the heavy fermion resistivity diminishes and moves to higher temperatures with increasing field. Direct comparison of the theoretical results to the field dependent resistivity measurements in CeB(6) yields good agreement.

  7. Angle-resolved heat capacity of heavy fermion superconductors

    NASA Astrophysics Data System (ADS)

    Sakakibara, Toshiro; Kittaka, Shunichiro; Machida, Kazushige

    2016-09-01

    Owing to a strong Coulomb repulsion, heavy electron superconductors mostly have anisotropic gap functions which have nodes for certain directions in the momentum space. Since the nodal structure is closely related to the pairing mechanism, its experimental determination is of primary importance. This article discusses the experimental methods of the gap determination by bulk heat capacity measurements in a rotating magnetic field. The basic idea is based on the fact that the quasiparticle density of states in the vortex state of nodal superconductors is field and direction dependent. We present our recent experimental results of the field-orientation dependence of the heat capacity in heavy fermion superconductors CeTIn5 (T  =  Co, Ir), UPt3, CeCu2Si2, and UBe13 and discuss their gap structures.

  8. Angle-resolved heat capacity of heavy fermion superconductors.

    PubMed

    Sakakibara, Toshiro; Kittaka, Shunichiro; Machida, Kazushige

    2016-09-01

    Owing to a strong Coulomb repulsion, heavy electron superconductors mostly have anisotropic gap functions which have nodes for certain directions in the momentum space. Since the nodal structure is closely related to the pairing mechanism, its experimental determination is of primary importance. This article discusses the experimental methods of the gap determination by bulk heat capacity measurements in a rotating magnetic field. The basic idea is based on the fact that the quasiparticle density of states in the vortex state of nodal superconductors is field and direction dependent. We present our recent experimental results of the field-orientation dependence of the heat capacity in heavy fermion superconductors CeTIn5 (T  =  Co, Ir), UPt3, CeCu2Si2, and UBe13 and discuss their gap structures.

  9. Interplay of Dirac fermions and heavy quasiparticles in solids.

    PubMed

    Höppner, M; Seiro, S; Chikina, A; Fedorov, A; Güttler, M; Danzenbächer, S; Generalov, A; Kummer, K; Patil, S; Molodtsov, S L; Kucherenko, Y; Geibel, C; Strocov, V N; Shi, M; Radovic, M; Schmitt, T; Laubschat, C; Vyalikh, D V

    2013-01-01

    Many-body interactions in crystalline solids can be conveniently described in terms of quasiparticles with strongly renormalized masses as compared with those of non-interacting particles. Examples of extreme mass renormalization are on the one hand graphene, where the charge carriers obey the linear dispersion relation of massless Dirac fermions, and on the other hand heavy-fermion materials where the effective electron mass approaches the mass of a proton. Here we show that both extremes, Dirac fermions, like they are found in graphene and extremely heavy quasiparticles characteristic for Kondo materials, may not only coexist in a solid but can also undergo strong mutual interactions. Using the example of EuRh₂Si₂, we explicitly demonstrate that these interactions can take place at the surface and in the bulk. The presence of the linear dispersion is imposed solely by the crystal symmetry, whereas the existence of heavy quasiparticles is caused by the localized nature of the 4f states.

  10. Millikelvin cooling by heavy-fermion-based tunnel junctions

    SciTech Connect

    Prest, Martin; Min, Gao; Whall, Terry

    2015-12-28

    This paper addresses a high-performance electron-tunneling cooler based on a novel heavy-fermion/insulator/superconductor junction for millikelvin cooling applications. We show that the cooling performance of an electronic tunneling refrigerator could be significantly improved using a heavy-fermion metal to replace the normal metal in a conventional normal metal/insulator/superconductor junction. The calculation, based on typical parameters, indicates that, for a bath temperature of 300 mK, the minimum cooling temperature of an electron tunneling refrigerator is reduced from around 170 mK to below 50 mK if a heavy-fermion metal is employed in place of the normal metal. The improved cooling is attributed to an enhancement in electron tunneling due to the existence of a resonant density of states at the Fermi level.

  11. Impurities in the heavy-Fermion superconductor UBe13

    NASA Astrophysics Data System (ADS)

    Smith, J. L.; Fisk, Z.; Willis, J. O.; Batlogg, B.; Ott, H. R.

    Small amounts of Sc, Lu, Gd, Np, Ce, Th, La, and Ba were substituted for uranium in UBe13 to observe their effects. The thorium, which was the most complete study, resulted in an extremely unusual nonmonotonic depression of the transition temperature for a nonmagnetic impurity. This comes from an interplay that exists between the lowest temperature resistivity peak and the transition temperature, as the peak is depressed. These results suggest that heavy Fermion behavior is only a necessary condition for heavy Fermion superconductivity. All of the impurities tested resulted in a transition temperature depression.

  12. Photoelectron spectroscopy in heavy fermions: Inconsistencies with the Kondo model

    SciTech Connect

    Arko, A.J.; Joyce, J.J.; Blyth, R.R.; Canfield, P.C.; Thompson, J.D.; Bartlett, R.J.; Fisk, Z.; Lawrence, J.; Tang, J.; Riseborough, P.

    1992-09-01

    We have investigated a number of Ce and Yb heavy fermion compounds via photoelectron spectroscopy and compared the results to the predictions of the Imurity Anderson Hamiltonian within the Gunnarson-Schonhammer approach. For the low T{sub K} materials investigated we find little or no correlation with T{sub K}, the only parameter that can be determined independent of photoemission.

  13. Magnitude of the magnetic exchange interaction in the heavy-fermion antiferromagnet CeRhIn₅.

    PubMed

    Das, Pinaki; Lin, S-Z; Ghimire, N J; Huang, K; Ronning, F; Bauer, E D; Thompson, J D; Batista, C D; Ehlers, G; Janoschek, M

    2014-12-12

    We have used high-resolution neutron spectroscopy experiments to determine the complete spin wave spectrum of the heavy-fermion antiferromagnet CeRhIn₅. The spin wave dispersion can be quantitatively reproduced with a simple frustrated J₁-J₂ model that also naturally explains the magnetic spin-spiral ground state of CeRhIn₅ and yields a dominant in-plane nearest-neighbor magnetic exchange constant J₀=0.74(3)  meV. Our results pave the way to a quantitative understanding of the rich low-temperature phase diagram of the prominent CeTIn₅ (T=Co, Rh, Ir) class of heavy-fermion materials.

  14. Magnitude of the magnetic exchange interaction in the heavy-fermion antiferromagnet CeRhIn5

    DOE PAGES

    Das, Pinaki; Lin, S. -Z.; Ghimire, N. J.; ...

    2014-12-08

    We have used high-resolution neutron spectroscopy experiments to determine the complete spin wave spectrum of the heavy-fermion antiferromagnet CeRhIn₅. The spin wave dispersion can be quantitatively reproduced with a simple frustrated J₁-J₂ model that also naturally explains the magnetic spin-spiral ground state of CeRhIn₅ and yields a dominant in-plane nearest-neighbor magnetic exchange constant J₀=0.74(3) meV. Our results lead the way to a quantitative understanding of the rich low-temperature phase diagram of the prominent CeTIn₅ (T = Co, Rh, Ir) class of heavy-fermion materials.

  15. Magnitude of the magnetic exchange interaction in the heavy-fermion antiferromagnet CeRhIn5

    SciTech Connect

    Das, Pinaki; Lin, S. -Z.; Ghimire, N. J.; Huang, K.; Ronning, F.; Bauer, E. D.; Thompson, J. D.; Batista, C. D.; Ehlers, G.; Janoschek, M.

    2014-12-08

    We have used high-resolution neutron spectroscopy experiments to determine the complete spin wave spectrum of the heavy-fermion antiferromagnet CeRhIn₅. The spin wave dispersion can be quantitatively reproduced with a simple frustrated J₁-J₂ model that also naturally explains the magnetic spin-spiral ground state of CeRhIn₅ and yields a dominant in-plane nearest-neighbor magnetic exchange constant J₀=0.74(3) meV. Our results lead the way to a quantitative understanding of the rich low-temperature phase diagram of the prominent CeTIn₅ (T = Co, Rh, Ir) class of heavy-fermion materials.

  16. (Strongly interacting fermion systems: Emphasis on heavy fermions: Annual performance report)

    SciTech Connect

    Not Available

    1987-01-01

    The research has been concentrated into two areas: heavy fermions and development of new methods for electronic properties (henceforth referred to as the ''electronic structure program''). This first area is going into deep hibernation due to the new interest in the high-T/sub c/ materials; notwithstanding this development, there has been significant progress. On the other hand, in the electronic structure program there has been a period of intense development which is just starting to yield results.

  17. High-pressure studies on heavy fermion systems

    NASA Astrophysics Data System (ADS)

    Ye, Chen; Zongfa, Weng; Smidman, Michael; Xin, Lu; Huiqiu, Yuan

    2016-07-01

    In this review article, we give a brief overview of heavy fermions, which are prototype examples of strongly correlated electron systems. We introduce the application of physical pressure in heavy fermion systems to construct their pressure phase diagrams and to study the close relationship between superconductivity (SC) and other electronic instabilities, such as antiferromagnetism (AFM), ferromagnetism (FM), and valence transitions. Field-angle dependent heat capacity and point-contact spectroscopic measurements under pressure are taken as examples to illustrate their ability to investigate novel physical properties of the emergent electronic states. Project supported by the National Basic Research Program of China (Grant No. 2011CBA00103), the National Natural Science Foundation of China (Grant Nos. 11174245 and 11374257), the Science Challenge Program of China, and the Fundamental Research Funds for the Central Universities of China.

  18. New heavy-fermion antiferromagnet UPd2Cd20.

    PubMed

    Hirose, Yusuke; Doto, Hiroshi; Honda, Fuminori; Li, Dexin; Aoki, Dai; Haga, Yoshinori; Settai, Rikio

    2016-10-26

    We succeeded in growing a new high quality single crystal of a ternary uranium compound UPd2Cd20. From the electrical resistivity, magnetization, magnetic susceptibility, and specific heat experiments, UPd2Cd20 is found to be an antiferromagnetic heavy-fermion compound with the Néel temperature [Formula: see text]  =  5 K and exhibits the large electronic specific heat coefficient γ exceeding 500 mJ (K(2)· mol)(-1). This compound is the first one that exhibits the magnetic ordering with the magnetic moments of the U atom in a series of UT2X20 (T: transition metal, X  =  Al, Zn, Cd). UPd2Cd20 shows typical characteristic features in heavy-fermion systems such as a broad maximum in the magnetic susceptibility at [Formula: see text] and a large coefficient A of T (2) term in the resistivity.

  19. First-principle Simulations of Heavy Fermion Materials

    NASA Astrophysics Data System (ADS)

    Dong, Ruanchen

    Heavy fermion materials, one of the most challenging topics in condensed matter physics, pose a variety of interesting properties and have attracted extensive studies for decades. Although there has been great success in explaining many ground- state properties of solids, the well-known theoretical calculations based on density functional theory (DFT) in its popular local density approximation (LDA) fail to describe heavy fermion materials due to improper treatment of many-body correlation effects. Here with the implementations of dynamical mean-field theory (DMFT) and the Gutzwiller variational method, the computational simulation of the heavy fermion materials is explored further and better compared with experimental data. In this dissertation, first, the theoretical background of DMFT and LDA+G methods is described in detail. The rest is the application of these techniques and is basically divided into two parts. First, the continuous-time quantum Monte Carlo (CT-QMC) method combined with DMFT is used to calculate and compare both the periodic Anderson model (PAM) and the Kondo lattice model (KLM). Different parameter sets of both models are connected by the Schrieffer-Wolff transformation. For spin and orbital degeneracy N = 2 case, a special particle-hole symmetric case of PAM at half-filling which always fixes one electron per impurity site is compared with the results of the KLM. We find a good mapping between PAM and KLM in the limit of large on-site Hubbard interaction U for different properties like self-energy, quasiparticle residue and susceptibility. This allows us to extract quasiparticle mass renormalizations for the f-electrons directly from KLM. The method is further applied to higher degenerate cases and to the realistic heavy fermion system CeRhIn5 in which the estimate of the Sommerfeld coefficient is proven to be close to the experimental value. Second, a series of Cerium based heavy fermion materials is studied using a combination of local

  20. Heavy fermions: From nodal metals to super-spins

    NASA Astrophysics Data System (ADS)

    Ramires Neves de Oliveira, Aline

    Condensed matter physics is an area of research which lies at a sweet spot between two complementary perspectives: the atomistic point of view which takes into account all the details of the system of interest; and the framework of universality and emergent phenomena, which allows us to make drastic simplifications to the microscopic description of materials while still being able to explain much of the experimentally observed phenomena. This thesis addresses problems from both perspectives, focusing on heavy fermion systems. Heavy fermion systems are prototype materials for the study of strongly correlations and quantum criticality. Theoretical understanding of these systems is important for the design of new materials and for the fundamental understanding of quantum critical phenomena. This thesis is strongly motivated by recent experiments in an intrinsically quantum critical material, beta-YbAlB 4. This system shows anomalous critical exponents in transport and thermodynamics. In Chapter 2 we construct a phenomenological theory for the heavy fermion metal beta-YbAlB4 based on the Anderson model, taking into account the peculiarities of this specific material. We analyze the consequences of a non-trivial, momentum-dependent, hybridization matrix between f-electrons and conduction electrons, which gives rise to a nodal metal with unusual dispersion and singular thermodynamic properties, in accordance with experiments. In Chapter 3 we analyze the Electron Spin Resonance experiments in this same material and propose a theory including spin-orbit coupling, crystal electric fields and hyperfine coupling which can account for many of the features of the experimentally observed signal. Within a broader perspective on heavy fermion systems, the absence of a single unified theoretical description which can account for the plethora of phenomena observed in this class of materials also motivates us to consider new theoretical approaches. In Chapter 4 we generalize the

  1. Strong coupling theory of heavy fermion criticality II

    NASA Astrophysics Data System (ADS)

    Wölfle, Peter; Schmalian, Jörg; Abrahams, Elihu

    2017-04-01

    We present a theory of the scaling behavior of the thermodynamic, transport and dynamical properties of a three-dimensional metal governed by d-dimensional fluctuations at a quantum critical point, where the electron quasiparticle effective mass diverges. We determine how the critical bosonic order parameter fluctuations are affected by the effective mass divergence. The coupled system of fermions and bosons is found to be governed by two stable fixed points: the conventional weak-coupling fixed point and a new strong-coupling fixed point, provided the boson–boson interaction is irrelevant. The latter fixed point supports hyperscaling, characterized by fractional exponents. The theory is applied to the antiferromagnetic critical point in certain heavy fermion compounds, in which the strong-coupling regime is reached.

  2. Strong coupling theory of heavy fermion criticality II.

    PubMed

    Wölfle, Peter; Schmalian, Jörg; Abrahams, Elihu

    2017-04-01

    We present a theory of the scaling behavior of the thermodynamic, transport and dynamical properties of a three-dimensional metal governed by d-dimensional fluctuations at a quantum critical point, where the electron quasiparticle effective mass diverges. We determine how the critical bosonic order parameter fluctuations are affected by the effective mass divergence. The coupled system of fermions and bosons is found to be governed by two stable fixed points: the conventional weak-coupling fixed point and a new strong-coupling fixed point, provided the boson-boson interaction is irrelevant. The latter fixed point supports hyperscaling, characterized by fractional exponents. The theory is applied to the antiferromagnetic critical point in certain heavy fermion compounds, in which the strong-coupling regime is reached.

  3. Is YbAs a heavy Fermion system

    SciTech Connect

    Monnier, R.; Degiorgi, L.; Delley, B.; Koelling, D.D. . Lab. fuer Festkoerperphysik; Paul Scherrer Inst. , Villigen; Argonne National Lab., IL )

    1989-08-01

    Using parameters extracted from a tight binding fit to an ab initio band structure, the specific heat anomaly observed in YbAs around 5 K is computed within the infinite U limit of the degenerate Anderson impurity model. Applying the renormalization procedure derived in variational treatments of the periodic Anderson model, a quasiparticle Fermi surface with strong nesting features and small mass enhancements is obtained. The results suggest that YbAs is not a classical'' heavy Fermion system. 28 refs., 3 figs., 1 tab.

  4. Nuclear Magnetic Resonance Studies in Heavy Fermion Materials

    NASA Astrophysics Data System (ADS)

    Shirer, Kent Robert

    29Si, 31P, and 115In nuclear magnetic resonance studies of heavy fermion materials URu2Si 2, CeRhIn5, and URu2Si2- xPx were conducted as a function of temperature, pressure, and, in the case of URu2Si2- xPx, doping. Knight shift measurements in these systems probe the hybridization between conduction and local f-electrons which is described by the heavy fermion coherence temperature, T*, and can be captured by a two fluid model. This model takes the dual nature of the local moments and the heavy electron fluid into account. In URu2Si2 in a pressure range from 0-9.1 kbar, spin-lattice-relaxation data were taken and suggest a partial suppression of the density of states below 30 K. The data are analyzed in terms of a two component spin-fermion model. The spin-lattice-relaxation behavior is then compared to other materials that demonstrate precursor fluctuations in a pseudogap regime above a ground state with long-range order. Nuclear magnetic resonance data in CeRhIn5 for both the In(1) and In(2) sites are also taken under hydrostatic pressure. The Knight shift data reveal a suppression of the hyperfine coupling to the In(1) site as a function of pressure, and the electric field gradient at the In(2) site exhibits a change of slope. These changes to these coupling constants reflect alterations to the electronic structure at the quantum critical point. Finally, we report 31P nuclear magnetic resonance measurements in single crystals of URu2Si2-xP x with x = 0.09, 0.33. In the case of the x = 0.09 doping, we find no evidence for a phase transition, though the material still exhibits heavy fermion coherence. In the x = 0.33 doping, we find that it undergoes an antiferromagnetic (AFM) phase transition. When we include the pure compound in our analysis, we find that the hyperfine couplings and coherence temperatures evolve with doping. We compare this evolution with the trends seen in other compounds.

  5. Emergent heavy fermion behavior at the Wigner-Mott transition.

    PubMed

    Merino, Jaime; Ralko, Arnaud; Fratini, Simone

    2013-09-20

    We study charge ordering driven by Coulomb interactions on triangular lattices relevant to the Wigner-Mott transition in two dimensions. Dynamical mean-field theory reveals the pinball liquid phase, a charge ordered metallic phase containing quasilocalized (pins) coexisting with itinerant (balls) electrons. Based on an effective periodic Anderson model for this phase, we find an antiferromagnetic Kondo coupling between pins and balls and strong quasiparticle renormalization. Non-Fermi liquid behavior can occur in such charge ordered systems due to the spin-flip scattering of itinerant electrons off the pins in analogy with heavy fermion compounds.

  6. Unconventional Quantum Criticality in Heavy-Fermion Compounds

    NASA Astrophysics Data System (ADS)

    Stockert, O.; Steglich, F.

    2011-03-01

    We review magnetic quantum-critical points (QPCs) in heavy-fermion compounds separating at zero temperature: an antiferromagnetically ordered state and a nonordered ground state. At the magnetic instability, the Fermi-liquid (FL) description valid for normal metals breaks down, giving rise to unusual, non-Fermi-liquid (NFL) low-temperature behavior. After a short introduction to phase transitions and to T = 0 phase transitions in general as well as to the physics of heavy-fermion systems, the two main theoretical scenarios describing the physics at QPCs in these systems are presented, the conventional spin-density-wave (SDW) scenario and the unconventional Kondo-breakdown scenario. Whereas for the conventional scenario experimental data for CeCu2Si2 and Ce1-xLaxRu2Si2 are discussed only briefly, we focus in more detail on the unusual behavior of CeCu6-xAux and YbRh2Si2 at their respective QPCs and show that these systems are best described within the unconventional scenario.

  7. Exploring heavy fermions from macroscopic to microscopic length scales

    NASA Astrophysics Data System (ADS)

    Wirth, Steffen; Steglich, Frank

    2016-10-01

    Strongly correlated systems present fundamental challenges, especially in materials in which electronic correlations cause a strong increase of the effective mass of the charge carriers. Heavy fermion metals — intermetallic compounds of rare earth metals (such as Ce, Sm and Yb) and actinides (such as U, Np and Pu) — are prototype systems for complex and collective quantum states; they exhibit both a lattice Kondo effect and antiferromagnetic correlations. These materials show unexpected phenomena; for example, they display unconventional superconductivity (beyond Bardeen-Cooper-Schrieffer (BCS) theory) and unconventional quantum criticality (beyond the Landau framework). In this Review, we focus on systems in which Landau's Fermi-liquid theory does not apply. Heavy fermion metals and semiconductors are well suited for the study of strong electronic correlations, because the relevant energy scales (for charge carriers, magnetic excitations and lattice dynamics) are well separated from each other, allowing the exploration of concomitant physical phenomena almost independently. Thus, the study of these materials also provides valuable insight for the understanding — and tailoring — of other correlated systems.

  8. Heavy-fermion instability in double-degenerate plasmas

    SciTech Connect

    Akbari-Moghanjoughi, M.

    2012-07-15

    In this work, we study the propagations of normal frequency modes for quantum hydrodynamic waves in the linear limit and introduce a new kind of instability in a double-degenerate plasma. Three different regimes, namely, low, intermediate, and high magnetic field strengths are considered which span the applicability of the work to a wide variety of environments. Distinct behavior is observed for different regimes, for instance, in the laboratory-scale field regime no frequency-mode instability occurs unlike those of intermediate and high magnetic-field strength regimes. It is also found that the instability of this kind is due to the heavy-fermions which appear below a critical effective-mass parameter ({mu}{sub cr}={radical}(3)) and that the responses of the two (lower and upper frequency) modes to fractional effective-mass change in different effective-mass parameter ranges (below and above the critical value) are quite opposite to each other. It is shown that the heavy-fermion instability due to extremely high magnetic field such as that encountered for a neutron-star crust can lead to confinement of stable propagations in both lower and upper frequency modes to the magnetic poles. Current study can have important implications for linear wave dynamics in both laboratory and astrophysical environments possessing high magnetic fields.

  9. Peltier effect in normal metal-insulator-heavy fermion metal junctions

    NASA Astrophysics Data System (ADS)

    Goltsev, A. V.; Rowe, D. M.; Kuznetsov, V. L.; Kuznetsova, L. A.; Min, Gao

    2003-04-01

    A theoretical study has been undertaken of the Peltier effect in normal metal-insulator-heavy fermion metal junctions. The results indicate that, at temperatures below the Kondo temperature, such junctions can be used as electronic microrefrigerators to cool the normal metal electrode and are several times more efficient in cooling than the normal metal-heavy fermion metal junctions.

  10. Optical spectra of the heavy fermion uniaxial ferromagnet UGe2

    NASA Astrophysics Data System (ADS)

    Guritanu, V.; Armitage, N. P.; Tediosi, R.; Saxena, S. S.; Huxley, A.; van der Marel, D.

    2008-11-01

    We report a detailed study of UGe2 single crystals using infrared reflectivity and spectroscopic ellipsometry. The optical conductivity suggests the presence of a low-frequency interband transition and a narrow free-carrier response with strong frequency dependence of the scattering rate and effective mass. We observe sharp increase in the low-frequency mass and reduction in scattering rate below the upper ferromagnetic transition TC=53K indicating the emergence of a heavy fermion state triggered by the ferromagnetic order. The characteristic changes are exhibited most strongly at an energy scale below 12 meV. They recover their unrenormalized value above TC and for ω>40meV . In contrast no sign of an anomaly is seen at the lower transition temperature of unknown nature, Tx˜30K , observed in transport and thermodynamic experiments.

  11. Phonon response of some heavy Fermion systems in dynamic limit

    NASA Astrophysics Data System (ADS)

    Sahoo, Jitendra; Shadangi, Namita; Nayak, Pratibindhya

    2017-05-01

    The phonon excitation spectrum of some Heavy Fermion (HF) systems in the presence of electron-phonon interaction is studied in the dynamic limit (ω≠0). The renormalized excitation phonon frequencies (ω˜ = ω/ω0) are evaluated through Periodic Anderson Model (PAM) in the presence of electron-phonon interaction using Zubarev-type double time temperature-dependent Green function. The calculated renormalized phonon energy is analyzed through the plots of (ω˜ = ω/ω0) against temperature for different system parameters like effective coupling strength ‘g’ and the position of f-level ‘d’. The observed behavior is analyzed and found to agree with the general features of HF systems found in experiments. Further, it is observed that in finite but small q-values the propagating phonons harden and change to localized peaks.

  12. Heavy fermion properties of the Kondo Lattice model

    PubMed Central

    Sykora, Steffen; Becker, Klaus W.

    2013-01-01

    We study the S = 1/2 Kondo lattice model which is widely used to describe heavy fermion behavior. In conventional treatments of the model the Kondo interaction is decoupled in favour of a hybridization of conduction and localized f electrons. However, such an approximation breaks the local gauge symmetry and implicates that the local f-occupation is no longer conserved. To avoid these problems, we use in this work an alternative approach to the model based on the Projective Renormalization Method (PRM). Thereby, within the conduction electron spectral function we identify the lattice Kondo resonance as an almost flat excitation near the Fermi surface which is composed of conduction electron creation operators combined with localized spin fluctuations. This leads to an alternative description of the Kondo resonance without having to resort to an artificial symmetry breaking. PMID:24045670

  13. Single crystal study of the heavy-fermion antiferromagnet CePt₂In₇.

    PubMed

    Tobash, Paul H; Ronning, F; Thompson, J D; Scott, B L; Moll, P J W; Batlogg, B; Bauer, E D

    2012-01-11

    We report the synthesis, structure, and physical properties of single crystals of CePt(2)In(7). Single crystal x-ray diffraction analysis confirms the tetragonal I4/mmm structure of CePt(2)In(7) with unit cell parameters a = 4.5886(6) Å, c = 21.530(6) Å and V = 453.32(14) Å(3). The magnetic susceptibility, heat capacity, Hall effect and electrical resistivity measurements are all consistent with CePt(2)In(7) undergoing an antiferromagnetic order transition at T(N) = 5.5 K, which is field independent up to 9 T. Above T(N), the Sommerfeld coefficient of specific heat is γ ≈ 300 mJ mol(-1) K(-2), which is characteristic of an enhanced effective mass of itinerant charge carriers. The electrical resistivity is typical of heavy-fermion behavior and gives a residual resistivity ρ(0) ∼ 0.2 µΩ cm, indicating good crystal quality. CePt(2)In(7) also shows moderate anisotropy of the physical properties that is comparable to structurally related CeMIn(5) (M = Co, Rh, Ir) heavy-fermion superconductors.

  14. Optical spectroscopy and ultrafast pump-probe studies on the heavy-fermion compound CePt2In7

    DOE PAGES

    Chen, R. Y.; Zhang, S. J.; Bauer, E. D.; ...

    2016-07-29

    We report optical spectroscopy and ultrafast pump-probe measurements on the antiferromagnetic heavy-fermion compound CePt 2 In 7 , a member showing stronger two dimensionality than other compounds in the CeIn 3 -derived heavy-fermion family. Here, we identify clear and typical hybridization spectral structures at low temperature from the two different spectroscopy probes. But, the strength and related energy scale of the hybridization are much weaker and smaller than that in the superconducting compounds CeCoIn 5 and CeIrIn 5 . The features are more similar to observations on the antiferromagnetic compounds CeIn 3 and CeRhIn 5 in the same family. Ourmore » results clearly indicate that the Kondo interaction and hybridizations exist in the antiferromagnetic compounds but with weaker strength.« less

  15. Polar Kerr effect studies of time reversal symmetry breaking states in heavy fermion superconductors

    SciTech Connect

    Schemm, E. R.; Levenson-Falk, E. M.; Kapitulnik, A.

    2016-11-30

    The connection between chiral superconductivity and topological order has emerged as an active direction in research as more instances of both have been identified in condensed matter systems. Moreover, with the notable exception of 3He-B, all of the known or suspected chiral – that is to say time-reversal symmetry-breaking (TRSB) – superfluids arise in heavy fermion superconductors, although the vast majority of heavy fermion superconductors preserve time-reversal symmetry. We review recent experimental efforts to identify TRSB states in heavy fermion systems via measurement of polar Kerr effect, which is a direct consequence of TRSB.

  16. Polar Kerr effect studies of time reversal symmetry breaking states in heavy fermion superconductors

    DOE PAGES

    Schemm, E. R.; Levenson-Falk, E. M.; Kapitulnik, A.

    2016-11-30

    The connection between chiral superconductivity and topological order has emerged as an active direction in research as more instances of both have been identified in condensed matter systems. Moreover, with the notable exception of 3He-B, all of the known or suspected chiral – that is to say time-reversal symmetry-breaking (TRSB) – superfluids arise in heavy fermion superconductors, although the vast majority of heavy fermion superconductors preserve time-reversal symmetry. We review recent experimental efforts to identify TRSB states in heavy fermion systems via measurement of polar Kerr effect, which is a direct consequence of TRSB.

  17. Polar Kerr effect studies of time reversal symmetry breaking states in heavy fermion superconductors

    NASA Astrophysics Data System (ADS)

    Schemm, E. R.; Levenson-Falk, E. M.; Kapitulnik, A.

    2017-04-01

    The connection between chiral superconductivity and topological order has emerged as an active direction in research as more instances of both have been identified in condensed matter systems. With the notable exception of 3He-B, all of the known or suspected chiral - that is to say time-reversal symmetry-breaking (TRSB) - superfluids arise in heavy fermion superconductors, although the vast majority of heavy fermion superconductors preserve time-reversal symmetry. Here we review recent experimental efforts to identify TRSB states in heavy fermion systems via measurement of polar Kerr effect, which is a direct consequence of TRSB.

  18. Tuning the dimensionality of the heavy fermion compound CeIn3.

    PubMed

    Shishido, H; Shibauchi, T; Yasu, K; Kato, T; Kontani, H; Terashima, T; Matsuda, Y

    2010-02-19

    Condensed-matter systems that are both low-dimensional and strongly interacting often exhibit unusual electronic properties. Strongly correlated electrons with greatly enhanced effective mass are present in heavy fermion compounds, whose electronic structure is essentially three-dimensional. We realized experimentally a two-dimensional heavy fermion system, adjusting the dimensionality in a controllable fashion. Artificial superlattices of the antiferromagnetic heavy fermion compound CeIn3 and the conventional metal LaIn3 were grown epitaxially. By reducing the thickness of the CeIn3 layers, the magnetic order was suppressed and the effective electron mass was further enhanced. Heavy fermions confined to two dimensions display striking deviations from the standard Fermi liquid low-temperature electronic properties, and these are associated with the dimensional tuning of quantum criticality.

  19. Photoemission and the electronic properties of heavy fermions -- limitations of the Kondo model

    SciTech Connect

    Joyce, J.J.; Arko, A.J.; Andrews, A.B.

    1993-09-01

    The electronic properties of Yb-based heavy fermions have been investigated by means of high resolution synchrotron radiation photoemission and compared with predictions of the Kondo model. The Yb heavy fermion photoemission spectra show massive disagreement with the Kondo model predictions (as calculated within the Gunnarsson-Schonhammer computational method). Moreover, the Yb heavy fermion photoemission spectra give very strong indications of core-like characteristics and compare favorable to purely divalent Yb metal and core-like Lu 4f levels. The heavy fermions YbCu{sub 2}Si{sub 2}, YbAgCu{sub 4} and YbAl{sub 3} were measured and shown to have lineshapes much broader and deeper in binding energy than predicted by the Kondo model. The lineshape of the bulk component of the 4f emission for these three heavy fermion materials was compared with that from Yb metal and the Lu 4f levels in LuAl{sub 3}, the heavy fermion materials show no substantive spectroscopic differences from simple 4f levels observed in Yb metal and LuAl{sub 3}. Also, the variation with temperature of the 4f fineshape was measured for Yb metal and clearly demonstrates that phonon broadening plays a major role in 4f level lineshape analysis and must be accounted for before considerations of correlated electron resonance effects are presumed to be at work.

  20. Spin gap in heavy fermion compound UBe13

    NASA Astrophysics Data System (ADS)

    Storchak, V. G.; Brewer, J. H.; Eshchenko, D. G.; Mengyan, P. W.; Parfenov, O. E.; Tokmachev, A. M.; Dosanjh, P.; Fisk, Z.; Smith, J. L.

    2016-08-01

    Heavy fermion (HF) compounds are well known for their unique properties, such as narrow bandwidths, loss of coherence in a metal, non-Fermi-liquid behaviour, unconventional superconductivity, huge magnetoresistance etc. While these materials have been known since the 1970s, there is still considerable uncertainty regarding the fundamental mechanisms responsible for some of these features. Here we report transverse-field muon spin rotation (μ +SR) experiments on the canonical HF compound UBe13 in the temperature range from 0.025 to 300 K and in magnetic fields up to 7 T. The μ +SR spectra exhibit a sharp anomaly at 180 K. We present a simple explanation of the experimental findings identifying this anomaly with a gap in the spin excitation spectrum of f-electrons opening near 180 K. It is consistent with anomalies discovered in heat capacity, NMR and optical conductivity measurements of UBe13, as well as with the new resistivity data presented here. The proposed physical picture may explain several long-standing mysteries of UBe13 (as well as other HF systems).

  1. NQR Study of the Heavy-Fermion Pu-115 Superconductors

    NASA Astrophysics Data System (ADS)

    Koutroulakis, G.; Yasuoka, H.; Tobash, P. H.; Mitchell, J. N.; Bauer, E. D.; Thompson, J. D.

    2014-03-01

    We present 115In nuclear quadrupolar resonance (NQR) measurements on the heavy-fermion superconductors Pu MIn5 (M=Co, Rh; Tc=2.5K, 1.6K, respectively), in the temperature range 0 . 29 K <= T <= 100 K . From the identified spectral lines, we deduce the quadrupolar parameters for the two inequivalent In sites, which are found to be qualitatively similar to those for other Ce- and Pu-115s. The quadrupolar frequency νQ varies with temperature in the normal state as per the empirical formula for conventional metals. As superconductivity develops, however, νQ exhibits a sharp, albeit small shift, which is a key prediction of the theory of composite superconducting (SC) pairing. The temperature variation of the nuclear spin-lattice relaxation rate T1- 1 delineates distinctive regimes of dynamic behavior. An excess of strong in-plane antiferromagnetic spin fluctuations is observed in the vicinity of Tc, which are believed to be playing a central role in the formation of the SC condensate. Analysis of the T1- 1 data in the SC state suggests that these compounds are strong-coupling d-wave superconductors.

  2. Inhomogeneous disorder Dirac Fermions: from heavy fermion superconductors to graphene. Final report

    SciTech Connect

    Vekhter, Ilya

    2013-08-11

    This is the final report on the award designed to foster a partnership between Louisiana State University and Los Alamos National Laboratory (LANL) in conducting fundamental research in support of energy needs. The general focus of the research effort was on developing a better understanding of materials with new functionalities. We investigated two distinct and very promising classes of new materials, which serve as a testing ground for many of the novel phenomena in condensed matter physics: the heavy fermion 115 series, where the interplay of strong interactions between the electrons leads to a rich variety of competing phases and anomalous properties, and newly discovered pnictide superconductors. The former focus was planned; the latter emerged during the collaborative effort with LANL. Our objective was to determine the origin, and to establish a functional effective theory description of the phases in these systems, and transitions between them. We report on the main accomplishments under the award that serves to clarify the nature of superconductivity in both families of materials. In particular, we collaborated with experimentalists to predict and analyze the magnetic field and temperature dependence of the bulk thermodynamic and transport properties and to determine the gap shape in CeCoIn₅ and in Ba(Fe1-xCox)₂As₂, investigated the Kondo temperature in the presence of spin-orbit coupling in the conduction band, and provided theoretical guidance for local probes such as scanning tunneling spectroscopy of vortex cores and impurity resonances, and magnetic force microscopy of the superconducting states.

  3. Superconductivity versus quantum criticality: what can we learn from heavy fermions?

    NASA Astrophysics Data System (ADS)

    Steglich, F.; Arndt, J.; Friedemann, S.; Krellner, C.; Tokiwa, Y.; Westerkamp, T.; Brando, M.; Gegenwart, P.; Geibel, C.; Wirth, S.; Stockert, O.

    2010-04-01

    Two quantum critical point (QCP) scenarios are being discussed for different classes of antiferromagnetic (AF) heavy-fermion (HF) systems. In the itinerant one, where AF order is of the spin-density wave (SDW) type, the heavy 'composite' charge carriers keep their integrity at the QCP. The second one implies a breakdown of the Kondo effect and a disintegration of the composite fermions at the AF QCP. We discuss two isostructural compounds as exemplary materials for these two different scenarios: CeCu2Si2 exhibits a three-dimensional (3D) SDW QCP and superconductivity, presumably mediated by SDW fluctuations, as strongly suggested by recent inelastic neutron scattering experiments. In Y bRh2Si2, the AF QCP is found to coincide with a Kondo-destroying one. However, in the latter compound these two QCPs can be detached by varying the average unit-cell volume, e.g. through the application of chemical pressure, as realized by partial substitution of either Ir or Co for Rh. A comparison of CeCu2Si2 and Y bRh2Si2 indicates that the apparent differences in quantum critical behaviour go along with disparate behaviour concerning the (non-) existence of superconductivity (SC). No sign of SC could be detected in Y bRh2Si2 down to mK temperatures. A potential correlation between the specific nature of the QCP and the occurrence of SC, however, requires detailed studies on further quantum critical HF superconductors, e.g. on β-Y bAlB4, UBe13, CeCoIn5 and CeRhIn5.

  4. Superconductivity versus quantum criticality: what can we learn from heavy fermions?

    PubMed

    Steglich, F; Arndt, J; Friedemann, S; Krellner, C; Tokiwa, Y; Westerkamp, T; Brando, M; Gegenwart, P; Geibel, C; Wirth, S; Stockert, O

    2010-04-28

    Two quantum critical point (QCP) scenarios are being discussed for different classes of antiferromagnetic (AF) heavy-fermion (HF) systems. In the itinerant one, where AF order is of the spin-density wave (SDW) type, the heavy 'composite' charge carriers keep their integrity at the QCP. The second one implies a breakdown of the Kondo effect and a disintegration of the composite fermions at the AF QCP. We discuss two isostructural compounds as exemplary materials for these two different scenarios: CeCu(2)Si(2) exhibits a three-dimensional (3D) SDW QCP and superconductivity, presumably mediated by SDW fluctuations, as strongly suggested by recent inelastic neutron scattering experiments. In Y bRh(2)Si(2), the AF QCP is found to coincide with a Kondo-destroying one. However, in the latter compound these two QCPs can be detached by varying the average unit-cell volume, e.g. through the application of chemical pressure, as realized by partial substitution of either Ir or Co for Rh. A comparison of CeCu(2)Si(2) and Y bRh(2)Si(2) indicates that the apparent differences in quantum critical behaviour go along with disparate behaviour concerning the (non-) existence of superconductivity (SC). No sign of SC could be detected in Y bRh(2)Si(2) down to mK temperatures. A potential correlation between the specific nature of the QCP and the occurrence of SC, however, requires detailed studies on further quantum critical HF superconductors, e.g. on β-Y bAlB(4), UBe(13), CeCoIn(5) and CeRhIn(5).

  5. Anomalies of magnetoresistance in Ce-based heavy fermion compounds

    NASA Astrophysics Data System (ADS)

    Sluchanko, N. E.; Bogach, A. V.; Anisimov, M. A.; Glushkov, V. V.; Demishev, S. V.; Samarin, N. A.; Chistyakov, O. D.; Burkhanov, G. S.; Gabani, S.; Flachbart, K.

    2015-12-01

    Magnetoresistance Δρ(H,T) of several heavy-fermion compounds, CeAl2, CeAl3 and CeCu6, substitutional solid solutions with quantum critical behavior CeCu6-xAux (x = 0.1, 0.2) and alloys with magnetic ground state Ce(Al1-xMx)2 (M = Co, Ni, x ≤ 0.8) was studied in a wide range of temperatures (1.8-40 K) in magnetic fields up to 80 kOe. It was shown that a consistent interpretation of the field dependences of the resistance for both non-magnetic and magnetically ordered cerium-based intermetallic compounds with strong electron correlations can be achieved within the framework of an approach that accounts for scattering of charge carriers by localized magnetic moments in a metal matrix. Within this approach, three different components of the magnetoresistance of cerium intermetallic compounds were identified: the negative Brillouin contribution proportional to the local magnetization ( -Δρ/ρ˜Mloc2 ), the alternating linear contribution ( Δρ/ρ˜H ) and the magnetic component, saturating in magnetic fields below 15 kOe. In the framework of the Yosida model for the cerium alloys under study, estimates of the local magnetic susceptibility χloc(H, T0) were obtained from the magnetoresistance data. Numerical differentiation of the magnetoresistance with respect to the magnetic field and analysis of the obtained d (Δρ/ρ)/d H =f (H ,T ) dependences allowed us to reconstruct the H-T magnetic phase diagrams of the strongly correlated electron systems under study as well as to examine the effects of spin polarization and renormalization of the electronic states on charge transport both in the regime of quantum critical behavior and in the magnetically ordered state.

  6. Fine tuning the heavy fermion ground state: A new handle on cerium cobalt indium

    NASA Astrophysics Data System (ADS)

    Pham, Long D.

    A Two Fluid Description of the Kondo Lattice CeCoIn5 has been extended to include additional entropy terms that were not considered in the original work by S. Nakatsuji et al. [1]. The use of a Matlab computer code was successful at iteratively solving for f, the fraction of itinerant interacting heavy quasiparticles, and showed that it converges to a temperature dependent function invariant under successive iterations. The linear specific heat coefficient, gamma, was extracted from transport consideration in conjunction with f(T) and the Kadowacki-Woods ratio to be 204mJ/mole-K2, in good agreement from heat capacity measurements of 290mJ/mole-K2 for CeCoIn 5 [32]. Antiferromagnetism has been induced in CeCoIn5 as well as its two isostructural, isovalent sister compounds CeRhIn5 and CeIrIn 5. Cadmium-doping the heavy-fermion superconductor CeCoIn5 at the percent level acts as an electronic tuning agent, sensitively shifting the balance between superconductivity and antiferromagnetism and opening new ambient-pressure phase space in the study of heavy-fermion ground states. At nominal concentrations of x>0.070, CeCo(In1-xCd x)5 displays a two phase region of antiferromagnetism coexisting with superconductivity up to x<0.15, above which no trace of superconductivity persists in specific heat. Similar results was seen in CeIr(In1-xCd x)5 where a quantum critical point (QCP) was observed, separating superconductivity from antiferromagnetism at a nominal critical concentration of x≈0.0475, while CeRh(In1-xCdx)5 goes through an incommensurate to commensurate antiferromagnetic transition nominally at x≈0.10. Amazingly, pressure completely recovers Tc in CeCo(In1-x Cdx)5 measured at nominal concentrations of x=0.10, and 0.15. Phase diagrams were constructed from specific heat and confirmed with resistivity and magnetization. An introduction to strongly correlated physics, relevant to the 115 family, will be worked out followed by a description of general techniques of

  7. Competition between heavy fermion and Kondo interaction in isoelectronic A-site-ordered perovskites.

    PubMed

    Meyers, D; Middey, S; Cheng, J-G; Mukherjee, Swarnakamal; Gray, B A; Cao, Yanwei; Zhou, J-S; Goodenough, J B; Choi, Yongseong; Haskel, D; Freeland, J W; Saha-Dasgupta, T; Chakhalian, J

    2014-12-17

    With current research efforts shifting towards the 4d and 5d transition metal oxides, understanding the evolution of the electronic and magnetic structure as one moves away from 3d materials is of critical importance. Here we perform X-ray spectroscopy and electronic structure calculations on A-site-ordered perovskites with Cu in the A-site and the B-sites descending along the ninth group of the periodic table to elucidate the emerging properties as d-orbitals change from partially filled 3d to 4d to 5d. The results show that when descending from Co to Ir, the charge transfers from the cuprate-like Zhang-Rice state on Cu to the t(2g) orbital of the B site. As the Cu d-orbital occupation approaches the Cu(2+) limit, a mixed valence state in CaCu(3)Rh(4)O(12) and heavy fermion state in CaCu(3)Ir(4)O(12) are obtained. The investigated d-electron compounds are mapped onto the Doniach phase diagram of the competing RKKY and Kondo interactions developed for the f-electron systems.

  8. Competition between heavy fermion and Kondo interaction in isoelectronic A-site-ordered perovskites

    SciTech Connect

    Meyers, D.; Middey, S.; Cheng, J.-G.; Mukherjee, Swarnakamal; Gray, B. A.; Cao, Yanwei; Zhou, J.-S.; Goodenough, J. B.; Choi, Yongseong; Haskel, D.; Freeland, J. W.; Saha-Dasgupta, T.; Chakhalian, J.

    2014-12-17

    With current research efforts shifting towards the 4d and 5d transition metal oxides, understanding the evolution of the electronic and magnetic structure as one moves away from 3d materials is of critical importance. Here we perform X-ray spectroscopy and electronic structure calculations on A-site-ordered perovskites with Cu in the A-site and the B-sites descending along the ninth group of the periodic table to elucidate the emerging properties as d-orbitals change from partially filled 3d to 4d to 5d. The results show that when descending from Co to Ir, the charge transfers from the cuprate-like Zhang-Rice state on Cu to the t2g orbital of the B site. As the Cu d-orbital occupation approaches the Cu2þ limit, a mixed valence state in CaCu3Rh4O12 and heavy fermion state in CaCu3Ir4O12 are obtained. The investigated d-electron compounds are mapped onto the Doniach phase diagram of the competing RKKY and Kondo interactions developed for the f-electron systems.

  9. How Kondo-holes create intense nanoscale heavy-fermion hybridization disorder

    PubMed Central

    Hamidian, Mohammad H.; Schmidt, Andrew R.; Firmo, Inês A.; Allan, Milan P.; Bradley, Phelim; Garrett, Jim D.; Williams, Travis J.; Luke, Graeme M.; Dubi, Yonatan; Balatsky, Alexander V.; Davis, J. C.

    2011-01-01

    Replacing a magnetic atom by a spinless atom in a heavy-fermion compound generates a quantum state often referred to as a “Kondo-hole”. No experimental imaging has been achieved of the atomic-scale electronic structure of a Kondo-hole, or of their destructive impact [Lawrence JM, et al. (1996) Phys Rev B 53:12559–12562] [Bauer ED, et al. (2011) Proc Natl Acad Sci. 108:6857–6861] on the hybridization process between conduction and localized electrons which generates the heavy-fermion state. Here we report visualization of the electronic structure at Kondo-holes created by substituting spinless thorium atoms for magnetic uranium atoms in the heavy-fermion system URu2Si2. At each thorium atom, an electronic bound state is observed. Moreover, surrounding each thorium atom we find the unusual modulations of hybridization strength recently predicted to occur at Kondo-holes [Figgins J, Morr DK (2011) Phys Rev Lett 107:066401]. Then, by introducing the “hybridization gapmap” technique to heavy-fermion studies, we discover intense nanoscale heterogeneity of hybridization due to a combination of the randomness of Kondo-hole sites and the long-range nature of the hybridization oscillations. These observations provide direct insight into both the microscopic processes of heavy-fermion forming hybridization and the macroscopic effects of Kondo-hole doping. PMID:22006302

  10. How Kondo-holes create intense nanoscale heavy-fermion hybridization disorder.

    PubMed

    Hamidian, Mohammad H; Schmidt, Andrew R; Firmo, Inês A; Allan, Milan P; Bradley, Phelim; Garrett, Jim D; Williams, Travis J; Luke, Graeme M; Dubi, Yonatan; Balatsky, Alexander V; Davis, J C

    2011-11-08

    Replacing a magnetic atom by a spinless atom in a heavy-fermion compound generates a quantum state often referred to as a "Kondo-hole". No experimental imaging has been achieved of the atomic-scale electronic structure of a Kondo-hole, or of their destructive impact [Lawrence JM, et al. (1996) Phys Rev B 53:12559-12562] [Bauer ED, et al. (2011) Proc Natl Acad Sci. 108:6857-6861] on the hybridization process between conduction and localized electrons which generates the heavy-fermion state. Here we report visualization of the electronic structure at Kondo-holes created by substituting spinless thorium atoms for magnetic uranium atoms in the heavy-fermion system URu(2)Si(2). At each thorium atom, an electronic bound state is observed. Moreover, surrounding each thorium atom we find the unusual modulations of hybridization strength recently predicted to occur at Kondo-holes [Figgins J, Morr DK (2011) Phys Rev Lett 107:066401]. Then, by introducing the "hybridization gapmap" technique to heavy-fermion studies, we discover intense nanoscale heterogeneity of hybridization due to a combination of the randomness of Kondo-hole sites and the long-range nature of the hybridization oscillations. These observations provide direct insight into both the microscopic processes of heavy-fermion forming hybridization and the macroscopic effects of Kondo-hole doping.

  11. Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics

    NASA Astrophysics Data System (ADS)

    Steglich, Frank; Wirth, Steffen

    2016-08-01

    This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a ‘conventional’, itinerant QCP can be well understood within Landau’s paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an ‘unconventional’, local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.

  12. Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics.

    PubMed

    Steglich, Frank; Wirth, Steffen

    2016-08-01

    This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a 'conventional', itinerant QCP can be well understood within Landau's paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an 'unconventional', local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.

  13. Impurities in the heavy-Fermion superconductor UBe/sub 13/

    SciTech Connect

    Smith, J.L.; Fisk, Z.; Willis, J.O.; Batlogg, B.; Ott, H.R.

    1983-01-01

    Small amounts of Sc, Lu, Gd, Np, Ce, Th, La, and Ba have been substituted for uranium in UBe/sub 13/ to observe their effects. The thorium, which was the most complete study, resulted in an extremely unusual nonmonotonic depression of the transition temperature for a nonmagnetic impurity. This comes from an interplay that exists between the lowest temperature resistivity peak and the transition temperature, as the peak is depressed. These results suggest tat heavy Fermion behavior is only a necessary condition for heavy Fermion superconductivity. All of the impurities tested resulted in a transition temperature depression.

  14. Heavy Weyl Fermion State in CeRu4Sn6

    NASA Astrophysics Data System (ADS)

    Xu, Yuanfeng; Yue, Changming; Weng, Hongming; Dai, Xi

    2017-01-01

    A new type of topological state in strongly correlated condensed matter systems, the heavy Weyl fermion state, has been found in a heavy fermion material, CeRu4Sn6, which has no inversion symmetry. Two different types of Weyl points, types I and II, can be found in the quasiparticle band structure obtained by the LDA +Gutzwiller calculations, which can treat the strong correlation effects among the f electrons from cerium atoms. The surface calculations indicate that the topologically protected Fermi arc states exist on the (010) but not on the (001) surface.

  15. Final Technical Report, Grant DE-FG02-91ER45443: Heavy fermions and other highly correlated electron systems

    SciTech Connect

    Schlottmann, P.

    1998-10-12

    Properties of highly correlated electrons, such as heavy fermion compounds, metal-insulator transitions, one-dimensional conductors and systems of restricted dimensionality are studied theoretically. The main focus is on Kondo insulators and impurity bands due to Kondo holes, the low-temperature magnetoresistivity of heavy fermion alloys, the n-channel Kondo problem, mesoscopic systems and one-dimensional conductors.

  16. Correlation between ground state and orbital anisotropy in heavy fermion materials

    SciTech Connect

    Willers, Thomas; Strigari, Fabio; Hu, Zhiwei; Sessi, Violetta; Brookes, Nicholas B.; Bauer, Eric D.; Sarrao, John L.; Thompson, J. D.; Tanaka, Arata; Wirth, Steffen; Tjeng, Liu Hao; Severing, Andrea

    2015-02-09

    The interplay of structural, orbital, charge, and spin degrees of freedom is at the heart of many emergent phenomena, including superconductivity. We find that unraveling the underlying forces of such novel phases is a great challenge because it not only requires understanding each of these degrees of freedom, it also involves accounting for the interplay between them. Cerium-based heavy fermion compounds are an ideal playground for investigating these interdependencies, and we present evidence for a correlation between orbital anisotropy and the ground states in a representative family of materials. We have measured the 4f crystal-electric field ground-state wave functions of the strongly correlated materials CeRh1₋xIrxIn5 with great accuracy using linear polarization-dependent soft X-ray absorption spectroscopy. These measurements show that these wave functions correlate with the ground-state properties of the substitution series, which covers long-range antiferromagnetic order, unconventional superconductivity, and coexistence of these two states.

  17. Doping study of the heavy fermion superconductor CePt2In7

    NASA Astrophysics Data System (ADS)

    Ghimire, Nirmal; Ronning, Filip; Thompson, J.; Bauer, Eric

    2014-03-01

    The CeMIn5 (M =Co, Rh, Ir) materials are prototypical heavy fermion superconductors close to antiferromagnetism, making them ideal candidates to investigate the interplay of unconventional superconductivity and magnetism and to explore quantum criticality. CeRhIn5 displays all of the signatures of a material close to an antiferromagnetic quantum critical point (QCP): 1) the antiferromagnetism at TN = 3.8 K is suppressed under applied pressure at Pc =2.5 GPa, 2) non-Fermi liquid behavior in the electrical resistivity and specific heat is observed near Pc, and 3) a dome of unconventional superconductivity appears with Tc max =2.6 K. To investigate the nature of the quantum criticality in the CemMnIn3 m + 2 n family, we focus attention on the newest member, CePt2In7, with m =1 and n =2, where m and n are CeIn3 and MIn2 layers. Similar to its cousin CeRhIn5 (m =1, n =1), it shows a dome of superconductivity and signatures of quantum criticality under pressure in the vicinity of where the Neel temperature is suppressed at Pc =3 GPa. As an alternative to the application of pressure to access the QCP, we present the magnetic, thermal and transport properties of doped CePt2In7. Work at Los Alamos was performed under the auspices of the US DOE.

  18. Physical properties of the Ce2MAl7Ge4 heavy-fermion compounds (M=Co,Ir,Ni,Pd)

    SciTech Connect

    Ghimire, N. J.; Cary, S. K.; Eley, S.; Wakeham, N. A.; Rosa, P. F. S.; Albrecht-Schmitt, T.; Lee, Y.; Janoschek, M.; Brown, C. M.; Civale, L.; Thompson, J. D.; Ronning, F.; Bauer, E. D.

    2016-05-23

    Here, we report the synthesis, crystal structure, and characterization by means of single-crystal x-ray diffraction, neutron powder diffraction, and magnetic, thermal, and transport measurements of the new heavy-fermion compounds Ce2MAl7Ge4 (M=Co,Ir,Ni,Pd). These compounds crystallize in a noncentrosymmetric tetragonal space group P$\\bar{4}$21m, consisting of layers of square nets of Ce atoms separated by Ge-Al and M-Al-Ge blocks. Ce2CoAl7Ge4,Ce2IrAl7Ge4, and Ce2NiAl7Ge4 order magnetically below TM=1.8, 1.6, and 0.8 K, respectively. There is no evidence of magnetic ordering in Ce2PdAl7Ge4 down to 0.4 K. Furthermore, the small amount of entropy released in the magnetic state of Ce2MAl7Ge4 (M = Co, Ir, Ni) and the reduced specific heat jump at TM suggest a strong Kondo interaction in these materials. Ce2PdAl7Ge4 shows non-Fermi liquid behavior, possibly due to the presence of a nearby quantum critical point.

  19. Physical properties of the Ce2MAl7Ge4 heavy-fermion compounds (M=Co,Ir,Ni,Pd)

    SciTech Connect

    Ghimire, N. J.; Cary, S. K.; Eley, S.; Wakeham, N. A.; Rosa, P. F. S.; Albrecht-Schmitt, T.; Lee, Y.; Janoschek, M.; Brown, C. M.; Civale, L.; Thompson, J. D.; Ronning, F.; Bauer, E. D.

    2016-05-23

    Here, we report the synthesis, crystal structure, and characterization by means of single-crystal x-ray diffraction, neutron powder diffraction, and magnetic, thermal, and transport measurements of the new heavy-fermion compounds Ce2MAl7Ge4 (M=Co,Ir,Ni,Pd). These compounds crystallize in a noncentrosymmetric tetragonal space group P$\\bar{4}$21m, consisting of layers of square nets of Ce atoms separated by Ge-Al and M-Al-Ge blocks. Ce2CoAl7Ge4,Ce2IrAl7Ge4, and Ce2NiAl7Ge4 order magnetically below TM=1.8, 1.6, and 0.8 K, respectively. There is no evidence of magnetic ordering in Ce2PdAl7Ge4 down to 0.4 K. Furthermore, the small amount of entropy released in the magnetic state of Ce2MAl7Ge4 (M = Co, Ir, Ni) and the reduced specific heat jump at TM suggest a strong Kondo interaction in these materials. Ce2PdAl7Ge4 shows non-Fermi liquid behavior, possibly due to the presence of a nearby quantum critical point.

  20. Direct observation of how the heavy-fermion state develops in CeCoIn5

    NASA Astrophysics Data System (ADS)

    Chen, Q. Y.; Xu, D. F.; Niu, X. H.; Jiang, J.; Peng, R.; Xu, H. C.; Wen, C. H. P.; Ding, Z. F.; Huang, K.; Shu, L.; Zhang, Y. J.; Lee, H.; Strocov, V. N.; Shi, M.; Bisti, F.; Schmitt, T.; Huang, Y. B.; Dudin, P.; Lai, X. C.; Kirchner, S.; Yuan, H. Q.; Feng, D. L.

    2017-07-01

    Heavy-fermion systems share some of the strange metal phenomenology seen in other unconventional superconductors, providing a unique opportunity to set strange metals in a broader context. Central to understanding heavy-fermion systems is the interplay of localization and itinerancy. These materials acquire high electronic masses and a concomitant Fermi volume increase as the f electrons delocalize at low temperatures. However, despite the wide-spread acceptance of this view, a direct microscopic verification has been lacking. Here we report high-resolution angle-resolved photoemission measurements on CeCoIn5, a prototypical heavy-fermion compound, which spectroscopically resolve the development of band hybridization and the Fermi surface expansion over a wide temperature region. Unexpectedly, the localized-to-itinerant transition occurs at surprisingly high temperatures, yet f electrons are still largely localized even at the lowest temperature. These findings point to an unanticipated role played by crystal-field excitations in the strange metal behavior of CeCoIn5. Our results offer a comprehensive experimental picture of the heavy-fermion formation, setting the stage for understanding the emergent properties, including unconventional superconductivity, in this and related materials.

  1. Landau Renormalizations of Superfluid Density in the Heavy-Fermion Superconductor CeCoIn5

    NASA Astrophysics Data System (ADS)

    Shu, Lei; MacLaughlin, D. E.; Varma, C. M.; Bernal, O. O.; Ho, P.-C.; Fukuda, R. H.; Shen, X. P.; Maple, M. B.

    2014-10-01

    The formation of heavy-fermion bands can occur by means of the conversion of a periodic array of local moments into itinerant electrons via the Kondo effect and the huge consequent Fermi-liquid renormalizations. Leggett predicted for liquid He3 that Fermi-liquid renormalizations change in the superconducting state, leading to a temperature dependence of the London penetration depth Λ quite different from that in BCS theory. Using Leggett's theory, as modified for heavy fermions, it is possible to extract from the measured temperature dependence of Λ in high quality samples both Landau parameters F0s and F1s; this has never been accomplished before. A modification of the temperature dependence of the electronic specific heat Cel, related to that of Λ, is also expected. We have carefully determined the magnitude and temperature dependence of Λ in CeCoIn5 by muon spin relaxation rate measurements to obtain F0s=36±1 and F1s=1.2±0.3, and we find a consistent change in the temperature dependence of Cel. This, the first determination of F1s with a value ≪F0s in a heavy-fermion compound, tests the basic assumption of the theory of heavy fermions, that the frequency dependence of the self-energy is much more important than its momentum dependence.

  2. Multiple quantum phase transitions and superconductivity in Ce-based heavy fermions.

    PubMed

    Weng, Z F; Smidman, M; Jiao, L; Lu, Xin; Yuan, H Q

    2016-09-01

    Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom points to an intricate relationship between superconductivity and other electronic states, which is unique but also shares some common features with high temperature superconductivity. The magnetic order in heavy fermion compounds can be continuously suppressed by tuning external parameters to a quantum critical point, and the role of quantum criticality in determining the properties of heavy fermion systems is an important unresolved issue. Here we review the recent progress of studies on Ce based heavy fermion superconductors, with an emphasis on the superconductivity emerging on the edge of magnetic and charge instabilities as well as the quantum phase transitions which occur by tuning different parameters, such as pressure, magnetic field and doping. We discuss systems where multiple quantum critical points occur and whether they can be classified in a unified manner, in particular in terms of the evolution of the Fermi surface topology.

  3. In-NQR study of heavy fermion superconductor Ce2PdIn8 under pressure

    NASA Astrophysics Data System (ADS)

    Fukazawa, Hideto; Shimatani, Sho; Shigeta, Kazuhiko; Kohori, Yoh; Kaczorowski, Dariusz

    2015-03-01

    115In nuclear quadrupole resonance measurements were performed in the normal state of the heavy fermion superconductor Ce2PdIn8 under hydrostatic pressure up to about 2.3 GPa. The observed behavior of the spin-lattice relaxation rate revealed a systematic suppression of antiferromagnetic critical fluctuations with increasing pressure.

  4. Landau renormalizations of superfluid density in the heavy-fermion superconductor CeCoIn5.

    PubMed

    Shu, Lei; MacLaughlin, D E; Varma, C M; Bernal, O O; Ho, P-C; Fukuda, R H; Shen, X P; Maple, M B

    2014-10-17

    The formation of heavy-fermion bands can occur by means of the conversion of a periodic array of local moments into itinerant electrons via the Kondo effect and the huge consequent Fermi-liquid renormalizations. Leggett predicted for liquid (3)He that Fermi-liquid renormalizations change in the superconducting state, leading to a temperature dependence of the London penetration depth Λ quite different from that in BCS theory. Using Leggett's theory, as modified for heavy fermions, it is possible to extract from the measured temperature dependence of Λ in high quality samples both Landau parameters F(0)(s) and F(1)(s); this has never been accomplished before. A modification of the temperature dependence of the electronic specific heat C(el), related to that of Λ, is also expected. We have carefully determined the magnitude and temperature dependence of Λ in CeCoIn(5) by muon spin relaxation rate measurements to obtain F(0)(s) = 36 ± 1 and F(1)(s) = 1.2 ± 0.3, and we find a consistent change in the temperature dependence of C(el). This, the first determination of F(1)(s) with a value ≪ F(0)(s) in a heavy-fermion compound, tests the basic assumption of the theory of heavy fermions, that the frequency dependence of the self-energy is much more important than its momentum dependence.

  5. Theory of scanning tunneling spectroscopy: from Kondo impurities to heavy fermion materials

    NASA Astrophysics Data System (ADS)

    Morr, Dirk K.

    2017-01-01

    Kondo systems ranging from the single Kondo impurity to heavy fermion materials present us with a plethora of unconventional properties whose theoretical understanding is still one of the major open problems in condensed matter physics. Over the last few years, groundbreaking scanning tunneling spectroscopy (STS) experiments have provided unprecedented new insight into the electronic structure of Kondo systems. Interpreting the results of these experiments—the differential conductance and the quasi-particle interference spectrum—however, has been complicated by the fact that electrons tunneling from the STS tip into the system can tunnel either into the heavy magnetic moment or the light conduction band states. In this article, we briefly review the theoretical progress made in understanding how quantum interference between these two tunneling paths affects the experimental STS results. We show how this theoretical insight has allowed us to interpret the results of STS experiments on a series of heavy fermion materials providing detailed knowledge of their complex electronic structure. It is this knowledge that is a conditio sine qua non for developing a deeper understanding of the fascinating properties exhibited by heavy fermion materials, ranging from unconventional superconductivity to non-Fermi-liquid behavior in the vicinity of quantum critical points.

  6. Extended s-wave pairing symmetry on the triangular lattice heavy fermion system

    NASA Astrophysics Data System (ADS)

    Zhang, Lan; Wang, Yu-Feng; Zhong, Yin; Luo, Hong-Gang

    2015-10-01

    We investigate the pairing symmetry of the Kondo-Heisenberg model on triangular lattice, which is believed to capture the core competition of Kondo screening and local magnetic exchange interaction in heavy electron compounds. On the dominant background of the heavy fermion state, the introduction of the Heisenberg antiferromagnetic interaction ( J H ) leads to superconducting pairing instability. Depending on the strength of the interactions, it is found that the pairing symmetry favours an extended s-wave for small J H and high conduction electron density but a chiral d_{x^2 - y^2 } + id_{xy}-wave for large J H and low conduction electron density, which provides a phase diagram of pairing symmetry from the calculations of the ground-state energy. The transition between these two pairing symmetries is found to be first-order. Furthermore, we also analyze the phase diagram from the pairing strengths and find that the phase diagram obtained is qualitatively consistent with that based on the ground-state energy. In addition, we propose an effective single-band BCS Hamiltonian, which is able to describe the low-energy thermodynamic behaviors of the heavy fermion superconducting states. These results further deepen the understanding of the antiferromagnetic interaction which results in a geometric frustration for the model studied. Our work may provide a possible scenario to understand the pairing symmetry of the heavy fermion superconductivity, which is one of active issues in very recent years.

  7. Theory of scanning tunneling spectroscopy: from Kondo impurities to heavy fermion materials.

    PubMed

    Morr, Dirk K

    2017-01-01

    Kondo systems ranging from the single Kondo impurity to heavy fermion materials present us with a plethora of unconventional properties whose theoretical understanding is still one of the major open problems in condensed matter physics. Over the last few years, groundbreaking scanning tunneling spectroscopy (STS) experiments have provided unprecedented new insight into the electronic structure of Kondo systems. Interpreting the results of these experiments-the differential conductance and the quasi-particle interference spectrum-however, has been complicated by the fact that electrons tunneling from the STS tip into the system can tunnel either into the heavy magnetic moment or the light conduction band states. In this article, we briefly review the theoretical progress made in understanding how quantum interference between these two tunneling paths affects the experimental STS results. We show how this theoretical insight has allowed us to interpret the results of STS experiments on a series of heavy fermion materials providing detailed knowledge of their complex electronic structure. It is this knowledge that is a conditio sine qua non for developing a deeper understanding of the fascinating properties exhibited by heavy fermion materials, ranging from unconventional superconductivity to non-Fermi-liquid behavior in the vicinity of quantum critical points.

  8. Magnetism and superconductivity in heavy fermion superconductor CeCo (In0.97Cd0/03)5

    SciTech Connect

    Heffner, R H; Ohishi, K; Spehling, J; Macdougall, G J; Ito, T U; Higemoto, W; Amato, D; Andreica, D; Nieuwenhuys, G; Klauss, H H; Luke, G M; Thompson, J D; Bianchi, A D; Fisk, Z

    2008-01-01

    Zero field (ZF) and transverse field (TF) muon spin relaxtion and rotation ({mu}SR) experiments have been carried out in the Cd-doped heavy fermion super conductor CeCoIn{sub 5} to investigate its superconducting state.

  9. Many-body effects in heavy fermion compounds [sic]. Final technical report for period September 1984 - January 2001

    SciTech Connect

    Riseborough, Peter S.

    2002-05-01

    A theoretical investigation of many-body effects in Cerium and Uranium Heavy Fermion and Mixed Valent Compounds and their experimental manifestations in thermodynamic, transport, and spectroscopic properties is discussed in this report.

  10. Emergent magnetic anisotropy in the cubic heavy-fermion metal CeIn3

    NASA Astrophysics Data System (ADS)

    Moll, Philip J. W.; Helm, Toni; Zhang, Shang-Shun; Batista, Cristian D.; Harrison, Neil; McDonald, Ross D.; Winter, Laurel E.; Ramshaw, B. J.; Chan, Mun K.; Balakirev, Fedor F.; Batlogg, Bertram; Bauer, Eric D.; Ronning, Filip

    2017-08-01

    Metals containing cerium exhibit a diverse range of fascinating phenomena including heavy fermion behavior, quantum criticality, and novel states of matter such as unconventional superconductivity. The cubic system CeIn3 has attracted significant attention as a structurally isotropic Kondo lattice material possessing the minimum required complexity to still reveal this rich physics. By using magnetic fields with strengths comparable to the crystal field energy scale, we illustrate a strong field-induced anisotropy as a consequence of non-spherically symmetric spin interactions in the prototypical heavy fermion material CeIn3. This work demonstrates the importance of magnetic anisotropy in modeling f-electron materials when the orbital character of the 4f wavefunction changes (e.g., with pressure or composition). In addition, magnetic fields are shown to tune the effective hybridization and exchange interactions potentially leading to new exotic field tuned effects in f-based materials.

  11. Evidence for fully-gapped superconductivity in heavy-fermion CeCu2Si2

    NASA Astrophysics Data System (ADS)

    Kasahara, Y.; Terazawa, D.; Yamashita, T.; Onishi, T.; Tokiwa, Y.; Terashima, T.; Matsuda, Y.; Takenaka, T.; Mizukami, Y.; Shibauchi, T.; Wilcox, J.; Putzke, C.; Carrington, A.; Kittaka, S.; Sakakibara, T.; Jeevan, H. S.; Seiro, S.; Geibel, C.; Haga, Y.

    The discovery of superconductivity in heavy-fermion CeCu2Si2 in 1979 has opened a new playground for unconventional superconductivity in strongly-correlated systems. However, even in this archetypal heavy-fermion superconductor, the symmetry and the structure of the superconducting gap, which are intimately related to the paring mechanism, are still elusive. Here, to investigate the low-energy quasiparticle excitations in the superconducting state of CeCu2Si2(Tc = 0 . 6 K), we performed specific heat, thermal conductivity, and penetration depth measurements down to 60 mK. We found that specific heat and penetration depth exhibit exponential T-dependence at low T. Moreover, thermal conductivity has no residual T-linear term and shows little H-dependence. These behavior are in marked contrast to nodal superconductors. From the data taken with different experimental configurations, the detailed superconducting gap structure will be discussed.

  12. Experimental discrimination of coherent and incoherent behavior in heavy-fermion materials

    SciTech Connect

    Penney, T.; Milliken, F.P.; von Molnar, S.; Holtzberg, F.; Fisk, Z.

    1986-10-15

    The onset of heavy-fermion coherent-ground-state behavior is studied in CeCu/sub 6/ by the Hall-effect and magnetoresistance measurements. CeCu/sub 6/ is an ideal system for this study since the fermions are extremely heavy and the system does not become either magnetic or superconducting. The strong temperature dependence of the Hall effect sets the scale for the high-temperature, single-Kondo-impurity, incoherent regime, a broad transition region, and the very-low-temperature coherent regime. In contrast to the resistivity, which shows a gradual transition to the coherent state, the Hall effect shows a rather sharp feature at the onset of coherence.

  13. First Observation of Heavy Fermion Behavior in Ce-Based Icosahedral Approximant

    NASA Astrophysics Data System (ADS)

    Imura, Keiichiro; Nobe, Kohei; Deguchi, Kazuhiko; Matsunami, Masaharu; Miyazaki, Hidetoshi; Yasui, Akira; Ikenaga, Eiji; Sato, Noriaki K.

    2017-09-01

    Since the discovery of unconventional quantum criticality in the Au-Al-Yb quasicrystal and pressure-induced quantum criticality in its approximant, quasicrystals and approximants with an icosahedral cluster of atoms have attracted much attention. Here we report magnetic, thermodynamic, transport, and hard x-ray photoemission spectroscopy experiments on the Ce-based approximant Ag-In-Ce. These results indicate the heavy fermion behavior of the 4f electrons and provide convincing evidence of a magnetic phase transition into a spin-glass-like short-range-ordered state at a low temperature. The Ag-In-Ce alloy is the first Ce-based heavy fermion approximant to a Tsai-type quasicrystal. Reflecting its unique crystal structure, the approximant shows an electrical resistivity distinct from that of traditional Kondo lattices.

  14. Infrared properties of heavy fermions: evolution from weak to strong hybridizations

    NASA Astrophysics Data System (ADS)

    Chen, R. Y.; Wang, N. L.

    2016-06-01

    In this article, we review the charge excitations of heavy fermion compounds probed by infrared spectroscopy. The article is not meant to be a comprehensive survey of experimental investigations. Rather it focuses on the dependence of charge excitations on the hybridization strength. In this context, the infrared properties of the Ce m M n In3m+2n family are discussed in detail since the hybridization strengths differ dramatically in different members despite their similar lattice structures. Investigations on some mixed valent compounds are also presented, aiming to elucidate the generic trend of the evolution. In particular, we address the scaling between hybridization energy gap {{Δ }\\text{dir}} and hybridization strength \\tilde{V} (\\propto \\sqrt{W{{T}\\text{K}}} ) in a wide range of heavy fermion compounds, which demonstrates that the periodic Anderson model can generally and quantitatively describe the low-energy charge excitations.

  15. Berezinskii-Kosterlitz-Thouless transition to the superconducting state of heavy-fermion superlattices.

    PubMed

    She, Jian-Huang; Balatsky, Alexander V

    2012-08-17

    We propose an explanation of the superconducting transitions discovered in the heavy-fermion superlattices by Mizukami et al. [Nature Phys. 7, 849 (2011)] in terms of Berezinskii-Kosterlitz-Thouless (BKT) transition. We observe that the effective mass mismatch between the heavy-fermion superconductor and the normal metal regions provides an effective barrier that enables quasi-2D superconductivity in such systems. We show that the resistivity data, both with and without magnetic field, are consistent with BKT transition. Furthermore, we study the influence of a nearby magnetic quantum critical point on the vortex system and find that the vortex core energy can be significantly reduced due to magnetic fluctuations. Further reduction of the gap with decreasing number of layers is understood as a result of pair breaking effect of Yb ions at the interface.

  16. Spin-orbit fluctuations in frustrated heavy-fermion metal LiV(2)O(4).

    PubMed

    Tomiyasu, K; Iwasa, K; Ueda, H; Niitaka, S; Takagi, H; Ohira-Kawamura, S; Kikuchi, T; Inamura, Y; Nakajima, K; Yamada, K

    2014-12-05

    Spin fluctuations were studied over a wide momentum (ℏQ) and energy (E) space in the frustrated d-electron heavy-fermion metal LiV_{2}O_{4} by time-of-flight inelastic neutron scattering. We observed the overall Q-E evolutions near the characteristic Q=0.6  Å^{-1}  peak and found another weak broad magnetic peak around 2.4  Å^{-1}. The data are described by a simple response function, a partially delocalized magnetic form factor, and antiferromagnetic short-range spatial correlations, indicating that heavy-fermion formation is attributable to spin-orbit fluctuations with orbital hybridization.

  17. Spin fluctations and heavy fermions in the Kondo lattice

    SciTech Connect

    Khaliullin, G.G.

    1994-09-01

    This paper studies the spectrum of the spin and electronic excitations of the Kondo lattice at low temperatures. To avoid unphysical states, the Mattis {open_quotes}drone{close_quotes}-fermion representation for localized spins is employed. First, the known Fermi liquid properties of a single impurity are examined. The behavior of the correlator between a localized spin and the electron spin density at large distances shows that the effective interaction between electrons on the Fermi level and low-energy localized spin fluctuations scales as {rho}{sup {minus}1}, where {rho} is the band-state density. This fact is developed into a renormalization of the band spectrum in a periodic lattice. If the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between localized spins is much smaller than the Kondo fluctuation frequency {omega}{sub k}, the temperature of the crossover to the single-parameter Fermi liquid mode is determined by {omega}{sub k}. When the RKKY interaction becomes of order {omega}{sub k}, there is a new scale {omega}{sub sf}, the energy of the (antiferromagnetic) paramagnon mode, with {omega}{sub sf}{much_lt}{omega}{sub k}. Here the coherent Fermi liquid regime is realized only below a temperature T{sub coh} of order {omega}{sub sf}, while above T{sub coh} quasiparticle damping exhibits a linear temperature dependence. Finally, the nuclear-spin relaxation rate is calculated. 42 refs.

  18. Unconventional quantum criticality in the pressure-induced heavy-fermion superconductor CeRhIn₅.

    PubMed

    Park, Tuson; Sidorov, V A; Lee, H; Ronning, F; Bauer, E D; Sarrao, J L; Thompson, J D

    2011-03-09

    The lack of superconductivity in several candidate materials that exhibit a non-spin density wave quantum critical point has raised the question of whether the associated spectra of quantum fluctuations are beneficial to forming superconducting electron pairs. Here we discuss the possibility that the prototypical heavy-fermion antiferromagnet CeRhIn5 may be the first example of unconventional superconductors where superconductivity arises from Kondo-breakdown quantum criticality.

  19. Contribution of heavy bosons and fermions to the action for a Robertson-Walker metric

    NASA Astrophysics Data System (ADS)

    Kebede, Temesgen; Bander, Myron

    1992-05-01

    The contributions of heavy, spatially homogeneous, boson and fermion fields to the effective action for a Robertson-Walker space-time are calculated. For scale factors larger than the Compton wavelengths of the particles associated with these matter fields the equations of motion for this scale factor are the same as those for a matter-dominated universe. Some speculations about the forces driving the expansion of the very early Universe are presented.

  20. de Haas van Alphen perspective on the origin of heavy fermions in UPt3

    NASA Astrophysics Data System (ADS)

    Rourke, Patrick; McCollam, Alix; McMullan, Greg; Norman, Mike; Julian, Stephen; Huxley, Andrew

    2006-03-01

    Precise de Haas van Alphen (dHvA) oscillation measurements on the heavy fermion superconductor UPt3 are available as a function of magnetic field angle. It was recently proposed that the heavy quasiparticles in this material arise from the localization of two of the three 5f electrons of the U ions [Zwicknagl et al., PRB 65, 081103R (2002)]. The predicted Fermi surface topology however differs from traditional bandstructure calculations. We will focus on the experimentally observed angle dependence of the hole-like δ-orbit, as this appears difficult to reconcile with the Fermi surface of Zwicknagl et al.

  1. Two-Loop Fermionic Corrections to Heavy-Quark Pair Production: theQuark-Antiquark Channel

    SciTech Connect

    Bonciani, R.; Ferroglia, A.; Gehrmann, T.; Maitre, D.; Studerus, C.; /Zurich U.

    2008-08-01

    We evaluate the fermionic two-loop QCD corrections to the heavy-quark pair production process in the quark-antiquark channel. We obtain analytic results which are valid for any value of the Mandelstam invariants s and t, and of the heavy quark mass m. Our findings confirm previous results for the analytic evaluation in the small-mass limit and numerical results for the exact amplitude. We furthermore provide the expansion of the two-loop amplitude at the production threshold s {approx}> 4m{sup 2}.

  2. Yb-based heavy fermion compounds and field tuned quantum chemistry

    SciTech Connect

    Mun, Eundeok

    2010-01-01

    The motivation of this dissertation was to advance the study of Yb-based heavy fermion (HF) compounds especially ones related to quantum phase transitions. One of the topics of this work was the investigation of the interaction between the Kondo and crystalline electric field (CEF) energy scales in Yb-based HF systems by means of thermoelectric power (TEP) measurements. In these systems, the Kondo interaction and CEF excitations generally give rise to large anomalies such as maxima in ρ(T) and as minima in S(T). The TEP data were use to determine the evolution of Kondo and CEF energy scales upon varying transition metals for YbT2Zn20 (T = Fe, Ru, Os, Ir, Rh, and Co) compounds and applying magnetic fields for YbAgGe and YbPtBi. For YbT2Zn20 and YbPtBi, the Kondo and CEF energy scales could not be well separated in S(T), presumably because of small CEF level splittings. A similar effect was observed for the magnetic contribution to the resistivity. For YbAgGe, S(T) has been successfully applied to determine the Kondo and CEF energy scales due to the clear separation between the ground state and thermally excited CEF states. The Kondo temperature, TK, inferred from the local maximum in S(T), remains finite as magnetic field increases up to 140 kOe. In this dissertation we have examined the heavy quasi-particle behavior, found near the field tuned AFM quantum critical point (QCP), with YbAgGe and YbPtBi. Although the observed nFL behaviors in the vicinity of the QCP are different between YbAgGe and YbPtBi, the constructed H-T phase diagram including the two crossovers are similar. For both YbAgGe and YbPtBi, the details of the quantum criticality turn out to be complicated. We expect that YbPtBi will provide an additional example of field tuned quantum criticality, but clearly there are further experimental investigations left and more ideas needed to understand the basic physics of field-induced quantum

  3. Chiral heavy fermions in a two Higgs doublet model: 750 GeV resonance or not

    NASA Astrophysics Data System (ADS)

    Bar-Shalom, Shaouly; Soni, Amarjit

    2017-03-01

    We revisit models where a heavy chiral 4th generation doublet of fermions is embedded in a class of two Higgs doublets models (2HDM) with a discrete Z2 symmetry, which couples the ;heavy; scalar doublet only to the 4th generation fermions and the ;light; one to the Standard Model (SM) fermions - the so-called 4G2HDM introduced by us several years ago. We study the constraints imposed on the 4G2HDM from direct searches of heavy fermions, from precision electroweak data (PEWD) and from the measured production and decay signals of the 125 GeV scalar, which in the 4G2HDM corresponds to the lightest CP-even scalar h. We then show that the recently reported excess in the γγ spectrum around 750 GeV can be accommodated by the heavy CP-even scalar of the 4G2HDM, H, resulting in a unique choice of parameter space: negligible mixing (sin ⁡ α ≲ O (10-3)) between the two CP-even scalars h , H and heavy 4th generation quark and lepton masses mt‧ ,mb‧ ≲ 400 GeV and mν‧ ,mτ‧ ≳ 900 GeV, respectively. Whether or not the 750 GeV γγ resonance is confirmed, interesting phenomenology emerges in q‧ - Higgs systems (q‧ =t‧ ,b‧), that can be searched for at the LHC. For example, the heavy scalar states of the model, S = H , A ,H+, may have BR (S →qbar‧q‧) ∼ O (1), giving rise to observable qbar‧q‧ signals on resonance, followed by the flavor changing q‧ decays t‧ → uh (u = u , c) and/or b‧ → dh (d = d , s , b). This leads to rather distinct signatures, with or without charged leptons, of the form qbar‧q‧ →(nj + mb + ℓW) S (j and b being light and b-quark jets, respectively), with n + m + ℓ = 6- 8 and unique kinematic features. These high jet-multiplicity signals appear to be very challenging and may need new search strategies for detection of such heavy chiral quarks. It is also shown that the flavor structure of the 4G2HDM can easily accommodate the interesting recent indications of a percent-level branching ratio in the

  4. Lithium vanadium oxide: A heavy fermion transition metal oxide

    NASA Astrophysics Data System (ADS)

    Kondo, Shinichiro

    LiVsb2Osb4 has the face-centered-cubic normal-spinel structure and is a metal. The preparative method and characterization of high-purity polycrystalline samples are herein reported. The intrinsic susceptibility chi, electronic heat capacity Csbe, nuclear magnetic resonance and thermal expansion measurements revealed that LiVsb2Osb4 shows a crossover from high temperature T localized magnetic moment behavior to low-T heavy Fermi liquid behavior. chi follows the Curie-Weiss law above ˜50 K with a Curie constant corresponding to a V S=1/2 spin and g-factor ˜2. The Weiss temperature indicates antiferromagnetic interactions between V local moments. chi becomes nearly T independent below ˜30K with a shallow broad maximum at T≈16K. Field-cooled and zero-field-cooled magnetization measurements in low applied magnetic fields H=10{-}100 G from 1.8 to 50 K showed no evidence for spin-glass ordering. The small amounts of paramagnetic impurities (S=3/2 to 4) in the samples were characterized using low-T isothermal magnetization Mspobs(H) measurement data. The observed electronic heat capacity coefficient gammaequiv Csbe/T≈0.42 J/mol Ksp2 at 1 K is extraordinarily large for a transition metal compound, the Wilson ratio ≈1.7, and the Korringa ratio ≈0.5. X-ray and neutron diffraction measurements down to 4 K found no distortion from the cubic structure. Neutron diffraction and dilatometry measurements indicate a strong enhancement of the thermal expansion coefficient and Gruneisen parameter below ˜20 K. Muon spin relaxation for a magnetically pure sample showed no evidence of static magnetic ordering above 0.02 K. Superconductivity was not observed above 0.01 K. All these measurements are consistent with a heavy Fermi liquid (HF) interpretation at low T. Theories which apply to some conventional f-electron HF compounds, the Kondo and Coqblin-Schrieffer models, fail to self-consistently explain chi(T) and Csbe(T) of LiVsb2Osb4. Geometric frustration inherent in the V

  5. Antiferromagnetism in metals: from the cuprate superconductors to the heavy fermion materials

    NASA Astrophysics Data System (ADS)

    Sachdev, Subir; Metlitski, Max A.; Punk, Matthias

    2012-07-01

    The critical theory of the onset of antiferromagnetism in metals, with concomitant Fermi surface reconstruction, has recently been shown to be strongly coupled in two spatial dimensions. The onset of unconventional superconductivity near this critical point is reviewed: it involves a subtle interplay between the breakdown of fermionic quasiparticle excitations on the Fermi surface and the strong pairing glue provided by the antiferromagnetic fluctuations. The net result is a logarithm-squared enhancement of the pairing vertex for generic Fermi surfaces, with a universal dimensionless coefficient independent of the strength of interactions, which is expected to lead to superconductivity at the scale of the Fermi energy. We also discuss the possibility that the antiferromagnetic critical point can be replaced by an intermediate ‘fractionalized Fermi liquid’ phase, in which there is Fermi surface reconstruction but no long-range antiferromagnetic order. We discuss the relevance of this phase to the underdoped cuprates and the heavy fermion materials.

  6. Antiferromagnetism in metals: from the cuprate superconductors to the heavy fermion materials.

    PubMed

    Sachdev, Subir; Metlitski, Max A; Punk, Matthias

    2012-07-25

    The critical theory of the onset of antiferromagnetism in metals, with concomitant Fermi surface reconstruction, has recently been shown to be strongly coupled in two spatial dimensions. The onset of unconventional superconductivity near this critical point is reviewed: it involves a subtle interplay between the breakdown of fermionic quasiparticle excitations on the Fermi surface and the strong pairing glue provided by the antiferromagnetic fluctuations. The net result is a logarithm-squared enhancement of the pairing vertex for generic Fermi surfaces, with a universal dimensionless coefficient independent of the strength of interactions, which is expected to lead to superconductivity at the scale of the Fermi energy. We also discuss the possibility that the antiferromagnetic critical point can be replaced by an intermediate 'fractionalized Fermi liquid' phase, in which there is Fermi surface reconstruction but no long-range antiferromagnetic order. We discuss the relevance of this phase to the underdoped cuprates and the heavy fermion materials.

  7. Temperature dependence of hybridization gaps in metallic heavy-fermion systems.

    PubMed

    Yang, Xiaodong; Riseborough, Peter S; Durakiewicz, Tomasz

    2011-03-09

    There is evidence that a number of heavy-fermion/mixed-valence materials show hybridization gaps either at the Fermi energy or close to it. In the former case, a heavy-fermion semiconducting state ensues, and in the latter case, the system remains metallic at low temperatures. In either case, there are significant indications that the electronic structure is extremely temperature dependent. In particular, there is evidence from spectroscopic and transport properties that the gap closes at high temperatures and also that the heavy-quasiparticle bands disappear at high temperatures. The magnitudes of the gaps scale with the effective quasiparticle masses. We present a phenomenological model that exhibits a temperature dependence which is consistent with the above behavior. The model is based on a periodic array of Anderson impurities in which the electron correlations are represented by the coupling to bosons with Einstein spectra. The model can be approximately solved in a systematic manner. The solution consists of semi-analytic expressions which represent the temperature dependences of the coherent and incoherent structures in the electronic excitation spectra. We shall compare the hybridization gaps predicted by the theory for the metallic case and those inferred from photoemission experiments on UPd2Al3.

  8. Cerium heavy-fermion compounds near their T = 0 magnetic-non-magnetic boundary

    SciTech Connect

    Thompson, J.D.; Hundley, M.F.; Movshovich, R.; Sarrao, J.L.; Graf, T.; Uwatoko, Y.; Fisk, Z.; Fisher, R.A.; Phillips, N.E. |

    1997-12-01

    Measurements of the temperature-dependent specific heat and thermal expansion coefficient near a T = 0 magnetic-non-magnetic boundary, accessed in CeRh{sub 2}Si{sub 2} by application of pressure and in CeRh{sub 2{minus}x}Ru{sub x}Si{sub 2} at ambient pressure by chemical substitution, emphasize the role of disorder in producing non-Fermi-liquid behavior. Interestingly, superconductivity also develops near this boundary in some crystallographically-ordered Ce-based heavy-fermion compounds.

  9. 73Ge-NQR study of heavy-fermion compound CeNi2Ge2

    NASA Astrophysics Data System (ADS)

    Kawasaki, S.; Sada, T.; Miyoshi, T.; Kotegawa, H.; Mukuda, H.; Kitaoka, Y.; Kobayashi, T. C.; Fukuhara, T.; Maezawa, K.; Itoh, K. M.; Haller, E. E.

    2007-03-01

    We report 73Ge-nuclear-quadrupole resonance (NQR) study of heavy-fermion compound CeNi2Ge2. The temperature dependence of the 73Ge nuclear-spin-lattice-relaxation rate 1/T1 indicates the development of magnetic correlations and the formation of a Fermi-liquid state at temperatures lower than TFL=0.4 K, where 1/T1T is constant. The 1/T1T decrease below TcNQR=0.1 K, whereas resistance decreases below Tconset=0.2 K and does not become zero. These results indicate CeNi2Ge2 closely locates to a superconducting quantum critical point.

  10. Converting heat to electricity by a graphene stripe with heavy chiral fermions

    NASA Astrophysics Data System (ADS)

    Shafranjuk, Serhii E.

    2014-04-01

    A conversion of thermal energy into electricity is considered in the electrically polarized graphene stripes with zigzag edges where the heavy chiral fermion (HCF) states are formed. The stripes are characterized by a high electric conductance G e and by a significant Seebeck coefficient S. The electric current in the stripes is induced due to a non-equilibrium thermal injection of "hot" electrons. This thermoelectric generation process might be utilized for building of thermoelectric generators with an exceptionally high figure of merit ZδT ≫ 1 and with an appreciable electric power densities ~1 MW/cm2.

  11. Field-induced quantum fluctuations in the heavy fermion superconductor CeCu(2)Ge(2).

    PubMed

    Singh, D K; Thamizhavel, A; Lynn, J W; Dhar, S; Rodriguez-Rivera, J; Herman, T

    2011-01-01

    Quantum-mechanical fluctuations in strongly correlated electron systems cause unconventional phenomena such as non-Fermi liquid behavior, and arguably high temperature superconductivity. Here we report the discovery of a field-tuned quantum critical phenomenon in stoichiometric CeCu(2)Ge(2), a spin density wave ordered heavy fermion metal that exhibits unconventional superconductivity under ≃10 GPa of applied pressure. Our finding of the associated quantum critical spin fluctuations of the antiferromagnetic spin density wave order, dominating the local fluctuations due to single-site Kondo effect, provide new information about the underlying mechanism that can be important in understanding superconductivity in this novel compound.

  12. Quantum phases of the Shastry-Sutherland Kondo lattice: implications for the global phase diagram of heavy-fermion metals.

    PubMed

    Pixley, J H; Yu, Rong; Si, Qimiao

    2014-10-24

    Considerable recent theoretical and experimental effort has been devoted to the study of quantum criticality and novel phases of antiferromagnetic heavy-fermion metals. In particular, quantum phase transitions have been discovered in heavy-fermion compounds with geometrical frustration. These developments have motivated us to study the competition between the Ruderman-Kittel-Kasuya-Yosida and Kondo interactions on the Shastry-Sutherland lattice. We determine the zero-temperature phase diagram as a function of magnetic frustration and Kondo coupling within a slave-fermion approach. Pertinent phases include the valence bond solid and heavy Fermi liquid. In the presence of antiferromagnetic order, our zero-temperature phase diagram is remarkably similar to the global phase diagram proposed earlier based on general grounds. We discuss the implications of our results for the experiments on Yb2Pt2Pb and related compounds.

  13. Formation of the coherent heavy fermion liquid at the hidden order transition in URu2Si2.

    PubMed

    Chatterjee, Shouvik; Trinckauf, Jan; Hänke, Torben; Shai, Daniel E; Harter, John W; Williams, Travis J; Luke, Graeme M; Shen, Kyle M; Geck, Jochen

    2013-05-03

    We present high-resolution angle-resolved photoemission spectra of the heavy-fermion superconductor URu2Si2. Detailed measurements as a function of both photon energy and temperature allow us to disentangle a variety of spectral features, revealing the evolution of the low-energy electronic structure across the "hidden order" transition. Above the transition, our measurements reveal the existence of weakly dispersive states that exhibit a large scattering rate and do not appear to shift from above to below the Fermi level, as previously reported. Upon entering the hidden order phase, these states rapidly hybridize with light conduction band states and transform into a coherent heavy fermion liquid, coincident with a dramatic drop in the scattering rate. This evolution is in stark contrast with the gradual crossover expected in Kondo lattice systems, which we attribute to the coupling of the heavy fermion states to the hidden order parameter.

  14. Extended nuclear quadrupole resonance study of the heavy-fermion superconductor PuCoGa5

    NASA Astrophysics Data System (ADS)

    Koutroulakis, G.; Yasuoka, H.; Tobash, P. H.; Mitchell, J. N.; Bauer, E. D.; Thompson, J. D.

    2016-10-01

    PuCoGa5 has emerged as a prototypical heavy-fermion superconductor, with its transition temperature (Tc≃18.5 K) being the highest amongst such materials. Nonetheless, a clear description as to what drives the superconducting pairing is still lacking, rendered complicated by the notoriously intricate nature of plutonium's 5 f valence electrons. Here, we present a detailed Ga,7169 nuclear quadrupole resonance (NQR) study of PuCoGa5, concentrating on the system's normal state properties near to Tc and aiming to detect distinct signatures of possible pairing mechanisms. In particular, the quadrupole frequency and spin-lattice relaxation rate were measured for the two crystallographically inequivalent Ga sites and for both Ga isotopes, in the temperature range 1.6-300 K. No evidence of significant charge fluctuations is found from the NQR observables. On the contrary, the low-energy dynamics is dominated by anisotropic spin fluctuations with strong, nearly critical, in-plane character, which are effectively identical to the case of the sister compound PuCoIn5. These findings are discussed within the context of different theoretical proposals for the unconventional pairing mechanism in heavy-fermion superconductors.

  15. Single-crystal study on the heavy-fermion antiferromagnet UZn12

    NASA Astrophysics Data System (ADS)

    Gonçalves, A. P.; Estrela, P.; de Visser, A.; Lopes, E. B.; Catarino, I.; Bonfait, G.; Godinho, M.; Almeida, M.; Gnida, D.; Kaczorowski, D.

    2011-02-01

    Millimetre size UZn12 single crystals were grown by the high temperature solution growth method using zinc as the solvent. Single-crystal x-ray diffraction data confirm that this compound crystallizes in the hexagonal high temperature form of SmZn12 (S.G. P6/mmm) and points to a U1.01(1)Zn11.7(1) stoichiometry for the crystals, with ~ 4% of the U atoms being located at the 2c site due to the partial substitution of 4h Zn pairs. UZn12 orders antiferromagnetically at TN = 5.0(2) K, and the magnetization and resistivity measurements suggest that the magnetic moments are confined within the a-b plane. The Sommerfeld coefficient, derived from the paramagnetic region by the standard method, is γp≈200 mJ (mol K2) - 1, which definitely classifies UZn12 as a moderate heavy-fermion system. The heavy-fermion character of UZn12 is also manifested in the overall shape of temperature-dependent electrical resistivity that is dominated by a single-ion Kondo effect at high temperatures and coherent Kondo scattering at low temperatures. The paramagnetic magnetoresistivity isotherms can be fairly well superimposed onto each other using Schlottmann's scaling for the single-ion Kondo model, as expected for a Kondo system.

  16. Extended nuclear quadrupole resonance study of the heavy-fermion superconductor PuCoGa5

    DOE PAGES

    Koutroulakis, Georgios; Yasuoka, Hiroshi; Tobash, Paul H.; ...

    2016-10-10

    PuCoGa5 has emerged as a prototypical heavy-fermion superconductor, with its transition temperature (Tc ≃ 18.5 K) being the highest amongst such materials. Nonetheless, a clear description as to what drives the superconducting pairing is still lacking, rendered complicated by the notoriously intricate nature of plutonium's 5f valence electrons. Here, we present a detailed 69,71Ga nuclear quadrupole resonance (NQR) study of PuCoGa5, concentrating on the system's normal state properties near to Tc and aiming to detect distinct signatures of possible pairing mechanisms. In particular, the quadrupole frequency and spin-lattice relaxation rate were measured for the two crystallographically inequivalent Ga sites andmore » for both Ga isotopes, in the temperature range 1.6–300 K. No evidence of significant charge fluctuations is found from the NQR observables. On the contrary, the low-energy dynamics is dominated by anisotropic spin fluctuations with strong, nearly critical, in-plane character, which are effectively identical to the case of the sister compound PuCoIn5. Lastly, these findings are discussed within the context of different theoretical proposals for the unconventional pairing mechanism in heavy-fermion superconductors.« less

  17. Simulating heavy fermion physics in optical lattice: Periodic Anderson model with harmonic trapping potential

    NASA Astrophysics Data System (ADS)

    Zhong, Yin; Liu, Yu; Luo, Hong-Gang

    2017-10-01

    The periodic Anderson model (PAM), where local electron orbitals interplay with itinerant electronic carriers, plays an essential role in our understanding of heavy fermion materials. Motivated by recent proposals for simulating the Kondo lattice model (KLM) in terms of alkaline-earth metal atoms, we take another step toward the simulation of PAM, which includes the crucial charge/valence fluctuation of local f-electrons beyond purely low-energy spin fluctuation in the KLM. To realize PAM, a transition induced by a suitable laser between the electronic excited and ground state of alkaline-earth metal atoms (1 S 0⇌3 P 0) is introduced. This leads to effective hybridization between local electrons and conduction electrons in PAM. Generally, the SU( N) version of PAM can be realized by our proposal, which gives a unique opportunity to detect large- N physics without complexity in realistic materials. In the present work, high-temperature physical features of standard [ SU(2)] PAM with harmonic trapping potential are analyzed by quantum Monte Carlo and dynamic mean-field theory, where the Mott/orbital-selective Mott state was found to coexist with metallic states. Indications for near-future experiments are provided. We expect our theoretical proposal and (hopefully) forthcoming experiments will deepen our understanding of heavy fermion systems. At the same time, we hope these will trigger further studies on related Mott physics, quantum criticality, and non-trivial topology in both the inhomogeneous and nonequilibrium realms.

  18. Quantum oscillations in the heavy-fermion compound YbPtBi

    DOE PAGES

    Mun, E.; Bud'ko, S. L.; Lee, Y.; ...

    2015-08-01

    We present quantum oscillations observed in the heavy-fermion compound YbPtBi in magnetic fields far beyond its field-tuned, quantum critical point. Quantum oscillations are observed in magnetic fields as low as 60 kOe at 60 mK and up to temperatures as high as 3 K, which confirms the very high quality of the samples as well as the small effective mass of the conduction carriers far from the quantum critical point. Although the electronic specific heat coefficient of YbPtBi reaches ~7.4 J/molK2 in zero field, which is one of the highest effective mass values among heavy-fermion systems, we suppress it quicklymore » by an applied magnetic field. The quantum oscillations were used to extract the quasiparticle effective masses of the order of the bare electron mass, which is consistent with the behavior observed in specific heat measurements. Furthermore, such small effective masses at high fields can be understood by considering the suppression of Kondo screening.« less

  19. Quantum oscillations in the heavy-fermion compound YbPtBi

    SciTech Connect

    Mun, E.; Bud'ko, S. L.; Lee, Y.; Martin, C.; Tanatar, M. A.; Prozorov, R.; Canfield, P. C.

    2015-08-01

    We present quantum oscillations observed in the heavy-fermion compound YbPtBi in magnetic fields far beyond its field-tuned, quantum critical point. Quantum oscillations are observed in magnetic fields as low as 60 kOe at 60 mK and up to temperatures as high as 3 K, which confirms the very high quality of the samples as well as the small effective mass of the conduction carriers far from the quantum critical point. Although the electronic specific heat coefficient of YbPtBi reaches ~7.4 J/molK2 in zero field, which is one of the highest effective mass values among heavy-fermion systems, we suppress it quickly by an applied magnetic field. The quantum oscillations were used to extract the quasiparticle effective masses of the order of the bare electron mass, which is consistent with the behavior observed in specific heat measurements. Furthermore, such small effective masses at high fields can be understood by considering the suppression of Kondo screening.

  20. NMR study of heavy fermion compound EuNi2P2

    NASA Astrophysics Data System (ADS)

    Magishi, K.; Watanabe, R.; Hisada, A.; Saito, T.; Koyama, K.; Fujiwara, T.

    2015-03-01

    We report the results of 31P-nuclear magnetic resonance (NMR) measurements on heavy fermion compound EuNi2P2 in order to investigate the magnetic properties at low temperatures from a microscopic view point. The Knight shift has a negative value in an entire temperature range, and the absolute value increases with decreasing temperature but exhibits a broad maximum around 40 K, which is similar to the behavior of the magnetic susceptibility. Also, the nuclear spin-lattice relaxation rate 1/T1 is almost constant at high temperatures above 200 K, which is reminiscent of the relaxation mechanism dominated by the interaction of the 31P nucleus with fluctuating Eu-4f moments. Below 200 K, 1/T1 gradually decreases on cooling due to the change of the valence in the Eu ion. At low temperatures, 1/T1 does not obey the Korringa relation, in contrast to typical heavy fermion compounds. The nuclear spin-spin relaxation rate 1/T2 shows the similar behavior as 1/T1 at high temperatures. But, below 50 K, 1/T2 increases upon cooling due to the development of the magnetic excitation.

  1. Heavy-fermion superconductivity in the quadrupole ordered state of PrV2Al20.

    PubMed

    Tsujimoto, Masaki; Matsumoto, Yosuke; Tomita, Takahiro; Sakai, Akito; Nakatsuji, Satoru

    2014-12-31

    PrV2Al20 is a rare example of a heavy-fermion system based on strong hybridization between conduction electrons and nonmagnetic quadrupolar moments of the cubic Γ3 ground doublet. Here, we report that a high-quality single crystal of PrV2Al20 exhibits superconductivity at Tc=50  mK in the antiferroquadrupole-ordered state under ambient pressure. The heavy-fermion character of the superconductivity is evident from the specific heat jump of ΔC/T∼0.3  J/mol K(2) and the effective mass m*/m0∼140 estimated from the temperature dependence of the upper critical field. Furthermore, the high-quality single crystals exhibit double transitions at TQ=0.75  K and T*=0.65  K associated with quadrupole and octupole degrees of freedom of the Γ3 doublet. In the ordered state, the specific heat C/T shows a T(3) dependence, indicating the gapless mode associated with the quadrupole order, the octupole order, or both. The strong sensitivity to impurity of the superconductivity suggests unconventional character due to significant quadrupolar fluctuations.

  2. Single-crystal study on the heavy-fermion antiferromagnet UZn₁₂.

    PubMed

    Gonçalves, A P; Estrela, P; de Visser, A; Lopes, E B; Catarino, I; Bonfait, G; Godinho, M; Almeida, M; Gnida, D; Kaczorowski, D

    2011-02-02

    Millimetre size UZn(12) single crystals were grown by the high temperature solution growth method using zinc as the solvent. Single-crystal x-ray diffraction data confirm that this compound crystallizes in the hexagonal high temperature form of SmZn(12) (S.G. P6/mmm) and points to a U(1.01(1))Zn(11.7(1)) stoichiometry for the crystals, with ∼ 4% of the U atoms being located at the 2c site due to the partial substitution of 4h Zn pairs. UZn(12) orders antiferromagnetically at T(N) = 5.0(2) K, and the magnetization and resistivity measurements suggest that the magnetic moments are confined within the a-b plane. The Sommerfeld coefficient, derived from the paramagnetic region by the standard method, is γ(p)≈200 mJ (mol K(2))( - 1), which definitely classifies UZn(12) as a moderate heavy-fermion system. The heavy-fermion character of UZn(12) is also manifested in the overall shape of temperature-dependent electrical resistivity that is dominated by a single-ion Kondo effect at high temperatures and coherent Kondo scattering at low temperatures. The paramagnetic magnetoresistivity isotherms can be fairly well superimposed onto each other using Schlottmann's scaling for the single-ion Kondo model, as expected for a Kondo system.

  3. Resonant magnetic exciton mode in the heavy-fermion antiferromagnet CeB₆.

    PubMed

    Friemel, G; Li, Yuan; Dukhnenko, A V; Shitsevalova, N Y; Sluchanko, N E; Ivanov, A; Filipov, V B; Keimer, B; Inosov, D S

    2012-05-15

    Resonant magnetic excitations are recognised as hallmarks of unconventional superconductivity in copper oxides, iron pnictides and heavy-fermion compounds. Model calculations have related these modes to the microscopic properties of the pair wave function, but the mechanisms of their formation are still debated. Here we report the discovery of a similar resonant mode in the non-superconducting antiferromagnetic heavy-fermion metal CeB(6). Unlike conventional magnons, the mode is non-dispersive and is sharply peaked around a wave vector separate from those characterising the antiferromagnetic order. It is likely associated with a co-existing order parameter of the unusual antiferro-quadrupolar phase of CeB(6), which has long remained hidden to neutron-scattering probes. The mode energy increases continuously below the onset temperature for antiferromagnetism, in parallel to the opening of a nearly isotropic spin gap throughout the Brillouin zone. These attributes are similar to those of the resonant modes in unconventional superconductors. This unexpected commonality between the two disparate ground states indicates the dominance of itinerant spin dynamics in the ordered low-temperature phases of CeB(6) and throws new light on the interplay between antiferromagnetism, superconductivity and 'hidden' order parameters in correlated-electron materials.

  4. Heavy-fermion quantum criticality and destruction of the Kondo effect in a nickel oxypnictide.

    PubMed

    Luo, Yongkang; Pourovskii, Leonid; Rowley, S E; Li, Yuke; Feng, Chunmu; Georges, Antoine; Dai, Jianhui; Cao, Guanghan; Xu, Zhu'an; Si, Qimiao; Ong, N P

    2014-08-01

    A quantum critical point arises at a continuous transformation between distinct phases of matter at zero temperature. Studies in antiferromagnetic heavy-fermion materials have revealed that quantum criticality has several classes, with an unconventional type that involves a critical destruction of the Kondo entanglement. To understand such varieties, it is important to extend the materials basis beyond the usual setting of intermetallic compounds. Here we show that a nickel oxypnictide, CeNiAsO, exhibits a heavy-fermion antiferromagnetic quantum critical point as a function of either pressure or P/As substitution. At the quantum critical point, non-Fermi-liquid behaviour appears, which is accompanied by a divergent effective carrier mass. Across the quantum critical point, the low-temperature Hall coefficient undergoes a rapid sign change, suggesting a sudden jump of the Fermi surface and a destruction of the Kondo effect. Our results imply that the enormous materials basis for the oxypnictides, which has been so crucial in the search for high-temperature superconductivity, will also play a vital role in the effort to establish the universality classes of quantum criticality in strongly correlated electron systems.

  5. Heavy-fermion quantum criticality and destruction of the Kondo effect in a nickel oxypnictide

    NASA Astrophysics Data System (ADS)

    Luo, Yongkang; Pourovskii, Leonid; Rowley, S. E.; Li, Yuke; Feng, Chunmu; Georges, Antoine; Dai, Jianhui; Cao, Guanghan; Xu, Zhu'An; Si, Qimiao; Ong, N. P.

    2014-08-01

    A quantum critical point arises at a continuous transformation between distinct phases of matter at zero temperature. Studies in antiferromagnetic heavy-fermion materials have revealed that quantum criticality has several classes, with an unconventional type that involves a critical destruction of the Kondo entanglement. To understand such varieties, it is important to extend the materials basis beyond the usual setting of intermetallic compounds. Here we show that a nickel oxypnictide, CeNiAsO, exhibits a heavy-fermion antiferromagnetic quantum critical point as a function of either pressure or P/As substitution. At the quantum critical point, non-Fermi-liquid behaviour appears, which is accompanied by a divergent effective carrier mass. Across the quantum critical point, the low-temperature Hall coefficient undergoes a rapid sign change, suggesting a sudden jump of the Fermi surface and a destruction of the Kondo effect. Our results imply that the enormous materials basis for the oxypnictides, which has been so crucial in the search for high-temperature superconductivity, will also play a vital role in the effort to establish the universality classes of quantum criticality in strongly correlated electron systems.

  6. Visualizing nodal superconductivity and heavy fermion formation in CeCoIn5

    NASA Astrophysics Data System (ADS)

    Zhou, Brian

    2014-03-01

    In solids containing elements with f - orbitals, the interaction between f-electron spins and those of itinerant electrons leads to the development of low-energy excitations with heavy effective mass. Previously, we used the scanning tunneling microscope (STM) to visualize the scattering of quasiparticles and detect their mass enhancement with the lowering of temperature in the prototypical Ce-115 heavy fermion family. Tunneling into different surface terminations revealed the composite nature of these heavy excitations, arising from the entanglement of conduction and f electrons. Here, by extending our techniques to milli-Kelvin temperature and high magnetic field, we first observe a spectroscopic pseudogap in the tunneling density of states of the heavy quasiparticles both prior to superconductivity and also above the critical field, indicating the development of further correlations from which the unconventional superconducting state arises. Quasiparticle interference (QPI) measurements in the superconducting and normal states demonstrate the onset of strong particle-hole asymmetry in the superconducting state, dissimilar from previous STM QPI studies of gap symmetry. Nevertheless, we can directly pinpoint the d-wave nature of Cooper pairing through visualizing the spatial symmetry of quasi-particle bound states in the vicinity of atomic scale defects. Work done in the collaboration with R. E. Baumbach, J. D. Thompson, E. D. Bauer, and A. Yazdani. Primary financial support from DOE-BES.

  7. Destruction of the Kondo effect in the cubic heavy-fermion compound Ce3Pd20Si6.

    PubMed

    Custers, J; Lorenzer, K A; Müller, M; Prokofiev, A; Sidorenko, A; Winkler, H; Strydom, A M; Shimura, Y; Sakakibara, T; Yu, R; Si, Q; Paschen, S

    2012-01-10

    How ground states of quantum matter transform between one another reveals deep insights into the mechanisms stabilizing them. Correspondingly, quantum phase transitions are explored in numerous materials classes, with heavy-fermion compounds being among the most prominent ones. Recent studies in an anisotropic heavy-fermion compound have shown that different types of transitions are induced by variations of chemical or external pressure, raising the question of the extent to which heavy-fermion quantum criticality is universal. To make progress, it is essential to broaden both the materials basis and the microscopic parameter variety. Here, we identify a cubic heavy-fermion material as exhibiting a field-induced quantum phase transition, and show how the material can be used to explore one extreme of the dimensionality axis. The transition between two different ordered phases is accompanied by an abrupt change of Fermi surface, reminiscent of what happens across the field-induced antiferromagnetic to paramagnetic transition in the anisotropic YbRh2Si2. This finding leads to a materials-based global phase diagram--a precondition for a unified theoretical description.

  8. Microscopic theoretical study of frequency dependent dielectric constant of heavy fermion systems

    NASA Astrophysics Data System (ADS)

    Shadangi, Keshab Chandra; Rout, G. C.

    2017-05-01

    The dielectric polarization and the dielectric constant plays a vital role in the deciding the properties of the Heavy Fermion Systems. In the present communication we consider the periodic Anderson's Model which consists of conduction electron kinetic energy, localized f-electron kinetic energy and the hybridization between the conduction and localized electrons, besides the Coulomb correlation energy. We calculate dielectric polarization which involves two particle Green's functions which are calculated by using Zubarev's Green's function technique. Using the equations of motion of the fermion electron operators. Finally, the temperature and frequency dependent dielectric constant is calculated from the dielectric polarization function. The charge susceptibility and dielectric constant are computed numerically for different physical parameters like the position (Ef) of the f-electron level with respect to fermi level, the strength of the hybridization (V) between the conduction and localized f-electrons, Coulomb correlation potential temperature and optical phonon wave vector (q). The results will be discussed in a reference to the experimental observations of the dielectric constants.

  9. Magnetism and superconductivity driven by identical 4f states in a heavy-fermion metal

    PubMed Central

    Nair, Sunil; Stockert, O.; Witte, U.; Nicklas, M.; Schedler, R.; Kiefer, K.; Thompson, J. D.; Bianchi, A. D.; Fisk, Z.; Wirth, S.; Steglich, F.

    2010-01-01

    The apparently inimical relationship between magnetism and superconductivity has come under increasing scrutiny in a wide range of material classes, where the free energy landscape conspires to bring them in close proximity to each other. Particularly enigmatic is the case when these phases microscopically interpenetrate, though the manner in which this can be accomplished remains to be fully comprehended. Here, we present combined measurements of elastic neutron scattering, magnetotransport, and heat capacity on a prototypical heavy fermion system, in which antiferromagnetism and superconductivity are observed. Monitoring the response of these states to the presence of the other, as well as to external thermal and magnetic perturbations, points to the possibility that they emerge from different parts of the Fermi surface. Therefore, a single 4f state could be both localized and itinerant, thus accounting for the coexistence of magnetism and superconductivity. PMID:20457945

  10. Low-temperature antiferromagnetic ordering in the heavy-fermion metal YbPd

    NASA Astrophysics Data System (ADS)

    Tokiwa, Y.; Grüheit, S.; Jeevan, H. S.; Stingl, C.; Gegenwart, P.

    2011-01-01

    We investigate the low-temperature properties of YbPd by specific heat and thermal expansion measurements down to 0.1 K. This material crystallizes in a cubic CsCl-structure and four phase transitions at 125, 105, 1.9 and 0.5 K have been reported previously. The two transitions at higher temperature were suspected to be of structural origin, whereas the two low-T transitions are magnetic, confirmed by susceptibility measurements and Mössbauer spectroscopy. Our low temperature specific heat and thermal expansion data prove antiferromagnetic ordering at TN=1.9 K and an additional first-order antiferromagnetic transition at 0.6 K. The entropy reaches approximately half of Rln2 at 5 K, confirming a doublet ground state. The enhanced value of the Sommerfeld coefficient at 0.1 K suggests a classification of YbPd as a magnetically ordered heavy-fermion metal.

  11. Study of frequency- and temperature-dependent electrical transport in heavy fermion systems

    NASA Astrophysics Data System (ADS)

    Baral, P. C.

    2017-05-01

    This paper focuses on the frequency- and temperature-dependent electrical transport properties of heavy fermion (HF) systems. For this, Kondo lattice model (KLM) with Coulomb correlation between f-f electrons at the same site is considered. The Hamiltonian is treated in mean-field approximation (MFA) for the Kondo hybridization and Heisenberg-type interaction to get mean-field Hamiltonian and it is written after the Fourier transformation. The Hartree-Fock-type approximation is considered for the Coulomb repulsion between f-f electrons, the perturbed part of the Hamiltonian. The two Green’s functions for the conduction and f-electrons are calculated to define the self-energy. Then the frequency- and temperature-dependent optical conductivity and resistivity are calculated by using the Kubo’s formula within the linear dynamical response approach. They are studied by varying the model parameters. The anomalies and results obtained are compared with experimental data.

  12. Muon spin relaxation in the heavy fermion system UPt sub 3

    SciTech Connect

    Luke, G.M.; Le, L.P.; Sternlieb, B.J.; Wu, W.D.; Uemura, Y.J. ); Dalichaouch, Y.; Lee, B.W.; Maple, M.B.; Seaman, C.L. . Dept. of Physics Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, California ); Armstrong, P.E.; Ellis, R.W.; Fisk, Z. )

    1991-11-15

    We report muon spin rotation/relaxation ({mu}SR) measurements of the heavy fermion superconductor UPt{sub 3} in external fields {ital H}{sub ext}{parallel}{ital {cflx c}}. We find that the muon Knight shift is unchanged in the superconducting state, consistent with odd-parity pairing (such as {ital p} wave). The transverse field relaxation is observed to be strongly field dependent, decreasing with increasing field. Below {ital T}{sub {ital c}} the increase is barely detectable in an applied field of 4 kG{parallel}{ital {cflx c}}. On the basis of the high field measurements, we estimate the low temperature penetration depth to be {lambda}({ital T}{r arrow}0){ge} (R18)11 000 A.

  13. Dynamical Electroweak Symmetry Breaking with a Heavy Fermion in Light of Recent LHC Results

    DOE PAGES

    Hung, Pham Q.

    2013-01-01

    The recent announcement of a discovery of a possible Higgs-like particle—its spin and parity are yet to be determined—at the LHC with a mass of 126 GeV necessitates a fresh look at the nature of the electroweak symmetry breaking, in particular if this newly-discovered particle will turn out to have the quantum numbers of a Standard Model Higgs boson. Even if it were a 0 + scalar with the properties expected for a SM Higgs boson, there is still the quintessential hierarchy problem that one has to deal with and which, by itself, suggests a new physics energy scale aroundmore » 1 TeV. This paper presents a minireview of one possible scenario: the formation of a fermion-antifermion condensate coming from a very heavy fourth generation, carrying the quantum number of the SM Higgs field, and thus breaking the electroweak symmetry.« less

  14. Samarium monoxide epitaxial thin film as a possible heavy-fermion compound

    NASA Astrophysics Data System (ADS)

    Uchida, Yutaka; Kaminaga, Kenichi; Fukumura, Tomoteru; Hasegawa, Tetsuya

    2017-03-01

    SmO (001) epitaxial thin films were grown on YAl O3 (110) substrates by pulsed laser deposition method. X-ray photoemission spectroscopy indicated coexistence of S m2 + and S m3 + , suggesting a valence fluctuating state. A SmO thin film showed a metallic conductionlike SmO polycrystal in a previous study. However, a SmO thin film showed nonmonotonical temperature dependence at low temperature in contrast with the polycrystal. A local resistivity minimum was observed at 16 K, probably caused by the dense Kondo effect, and the resistivity below 2 K was proportional to T2. These features suggest the heavy-fermionic nature of SmO.

  15. Heavy fermions. Chirality density wave of the "hidden order" phase in URu₂Si₂.

    PubMed

    Kung, H-H; Baumbach, R E; Bauer, E D; Thorsmølle, V K; Zhang, W-L; Haule, K; Mydosh, J A; Blumberg, G

    2015-03-20

    A second-order phase transition in a physical system is associated with the emergence of an "order parameter" and a spontaneous symmetry breaking. The heavy fermion superconductor URu2Si2 has a "hidden order" (HO) phase below the temperature of 17.5 kelvin; the symmetry of the associated order parameter has remained ambiguous. Here we use polarization-resolved Raman spectroscopy to specify the symmetry of the low-energy excitations above and below the HO transition. We determine that the HO parameter breaks local vertical and diagonal reflection symmetries at the uranium sites, resulting in crystal field states with distinct chiral properties, which order to a commensurate chirality density wave ground state. Copyright © 2015, American Association for the Advancement of Science.

  16. Magnetism and superconductivity driven by identical 4f states in a heavy-fermion metal

    SciTech Connect

    Thompson, Joe E; Nair, S; Stockert, O; Witte, U; Nicklas, M; Schedler, R; Bianchi, A; Fisk, Z; Wirth, S; Steglich, K

    2009-01-01

    The apparently inimical relationship between magnetism and superconductivity has come under increasing scrutiny in a wide range of material classes, where the free energy landscape conspires to bring them in close proximity to each other. Particularly enigmatic is the case when these phases microscopically interpenetrate, though the manner in which this can be accomplished remains to be fully comprehended. Here, we present combined measurements of elastic neutron scattering, magnetotransport, and heat capacity on a prototypical heavy fermion system, in which antiferromagnetism and superconductivity are observed. Monitoring the response of these states to the presence of the other, as well as to external thermal and magnetic perturbations, points to the possibility that they emerge from different parts of the Fermi surface. Therefore, a single 4f state could be both localized and itinerant, thus accounting for the coexistence of magnetism and superconductivity.

  17. Magnetic and superconducting quantum critical points of heavy-fermion systems

    NASA Astrophysics Data System (ADS)

    Demuer, A.; Sheikin, I.; Braithwaite, D.; Fåk, B.; Huxley, A.; Raymond, S.; Flouquet, J.

    2001-05-01

    Two examples of heavy-fermion systems are presented : CePd 2Si 2, an antiferromagnet with a quantum critical point at PC=28 kbar and UGe 2 an itinerant ferromagnet which transits in a paramagnetic phase above PC=16 kbar. In CePd 2Si 2 the superconductivity domain is centered on PC. Special attention was given to the superconducting and magnetic anomalies at their superconducting and Néel temperatures. In UGe 2 superconductivity appears in 9 kbar at a temperature TS, more than two orders of magnitude lower than the Curie temperature; furthermore, it occurs only on the magnetic border ( P< PC). Another characteristic temperature TX is detected by resistivity; the zigzag uranium chain of the lattice may favor a supplementary nesting in the majority spin band.

  18. Direct observation of the quantum critical point in heavy fermion CeRhSi3.

    PubMed

    Egetenmeyer, N; Gavilano, J L; Maisuradze, A; Gerber, S; MacLaughlin, D E; Seyfarth, G; Andreica, D; Desilets-Benoit, A; Bianchi, A D; Baines, Ch; Khasanov, R; Fisk, Z; Kenzelmann, M

    2012-04-27

    We report on muon spin rotation studies of the noncentrosymmetric heavy fermion antiferromagnet CeRhSi3. A drastic and monotonic suppression of the internal fields, at the lowest measured temperature, was observed upon an increase of external pressure. Our data suggest that the ordered moments are gradually quenched with increasing pressure, in a manner different from the pressure dependence of the Néel temperature. At 23.6 kbar, the ordered magnetic moments are fully suppressed via a second-order phase transition, and T(N) is zero. Thus, we directly observed the quantum critical point at 23.6 kbar hidden inside the superconducting phase of CeRhSi3.

  19. Grüneisen parameter studies on heavy fermion quantum criticality

    NASA Astrophysics Data System (ADS)

    Gegenwart, Philipp

    2016-11-01

    The Grüneisen parameter, experimentally determined from the ratio of thermal expansion to specific heat, quantifies the pressure dependence of characteristic energy scales of matter. It is highly enhanced for Kondo lattice systems, whose properties are strongly dependent on the pressure sensitive antiferromagnetic exchange interaction between f- and conduction electrons. In this review, we focus on the divergence of the Grüneisen parameter and its magnetic analogue, the adiabatic magnetocaloric effect, for heavy-fermion metals near quantum critical points. We compare experimental results with current theoretical models, including the effect of strong geometrical frustration. We also discuss the possibility of using materials with the divergent magnetic Grüneisen parameter for adiabatic demagnetization cooling to very low temperatures.

  20. Study of frequency and temperature dependent electrical resistivity in heavy fermion systems

    NASA Astrophysics Data System (ADS)

    Baral, P. C.

    2017-07-01

    This paper focuses on the interplay of Kondo effect and magnetic ordering through a microscopic theory of the frequency and temperature dependent electrical resistivity as well as the dielectric function in heavy fermion systems. It is then analysed in Kondo lattice model in addition to Heisenberg-type interaction between localized f-electrons. The model Hamiltonian is solved by using mean-field approximation (MFA). The study of electrical resistivity is presented by considering phonon interaction to bare f-electrons, c-electrons and to the hybridization between c- and f-electrons and phonon Hamiltonian in harmonic approximation. An attempt has been made to calculate the temperature and frequency dependent electrical resistivity to study the peaks at TK (Kondo temperature) and T_{{ Cor}} (correlation temperature). The evolution of peaks exhibit change in slopes. These findings are compared to the experimental data.

  1. Study of frequency and temperature dependent electrical resistivity in heavy fermion systems

    NASA Astrophysics Data System (ADS)

    Baral, P. C.

    2017-02-01

    This paper focuses on the interplay of Kondo effect and magnetic ordering through a microscopic theory of the frequency and temperature dependent electrical resistivity as well as the dielectric function in heavy fermion systems. It is then analysed in Kondo lattice model in addition to Heisenberg-type interaction between localized f- electrons. The model Hamiltonian is solved by using mean-field approximation (MFA). The study of electrical resistivity is presented by considering phonon interaction to bare f -electrons, c -electrons and to the hybridization between c - and f -electrons and phonon Hamiltonian in harmonic approximation. An attempt has been made to calculate the temperature and frequency dependent electrical resistivity to study the peaks at TK (Kondo temperature) and T_{{ Cor}} (correlation temperature). The evolution of peaks exhibit change in slopes. These findings are compared to the experimental data.

  2. Interface between heavy fermions and normal electrons investigated by spatially resolved nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Yamanaka, Takayoshi; Shimozawa, Masaaki; Endo, Ryota; Mizukami, Yuta; Shishido, Hiroaki; Terashima, Takahito; Shibauchi, Takasada; Matsuda, Yuji; Ishida, Kenji

    2015-12-01

    We have studied the superlattices with alternating block layers (BLs) of heavy-fermion superconductor CeCoIn5 and conventional-metal YbCoIn5 by site-selective nuclear magnetic resonance spectroscopy, which uniquely offers spatially resolved dynamical magnetic information. We find that the presence of antiferromagnetic fluctuations is confined to the Ce BLs, indicating that magnetic degrees of freedom of f electrons are quenched inside the Yb BLs. Contrary to simple expectations that the two dimensionalization enhances fluctuations, we observe that antiferromagnetic fluctuations are rapidly suppressed with decreasing Ce BL thickness. Moreover, the suppression is more prominent near the interfaces between the BLs. These results imply significant effects of local inversion symmetry breaking at the interfaces.

  3. Superconductivity. Observation of broken time-reversal symmetry in the heavy-fermion superconductor UPt₃.

    PubMed

    Schemm, E R; Gannon, W J; Wishne, C M; Halperin, W P; Kapitulnik, A

    2014-07-11

    Models of superconductivity in unconventional materials can be experimentally differentiated by the predictions they make for the symmetries of the superconducting order parameter. In the case of the heavy-fermion superconductor UPt3, a key question is whether its multiple superconducting phases preserve or break time-reversal symmetry (TRS). We tested for asymmetry in the phase shift between left and right circularly polarized light reflected from a single crystal of UPt3 at normal incidence and found that this so-called polar Kerr effect appears only below the lower of the two zero-field superconducting transition temperatures. Our results provide evidence for broken TRS in the low-temperature superconducting phase of UPt3, implying a complex two-component order parameter for superconductivity in this system.

  4. Grüneisen parameter studies on heavy fermion quantum criticality.

    PubMed

    Gegenwart, Philipp

    2016-11-01

    The Grüneisen parameter, experimentally determined from the ratio of thermal expansion to specific heat, quantifies the pressure dependence of characteristic energy scales of matter. It is highly enhanced for Kondo lattice systems, whose properties are strongly dependent on the pressure sensitive antiferromagnetic exchange interaction between f- and conduction electrons. In this review, we focus on the divergence of the Grüneisen parameter and its magnetic analogue, the adiabatic magnetocaloric effect, for heavy-fermion metals near quantum critical points. We compare experimental results with current theoretical models, including the effect of strong geometrical frustration. We also discuss the possibility of using materials with the divergent magnetic Grüneisen parameter for adiabatic demagnetization cooling to very low temperatures.

  5. Fragile antiferromagnetism in the heavy-fermion compound YbBiPt

    SciTech Connect

    Ueland, Benjamin G.; Kreyssig, Andreas; Prokes, K.; Lynn, J. W.; Harriger, L. W.; Pratt, D. K.; Singh, D. K.; Heitmann, T. W.; Sauerbrei, Samantha; Saunders, Scott M.; Mun, E. D.; Budko, Serguei L.; McQueeney, Robert J.; Canfield, Paul C.; Goldman, Alan I.

    2014-05-08

    We report results from neutron scattering experiments on single crystals of YbBiPt that demonstrate antiferromagnetic order characterized by a propagation vector, τAFM = (121212), and ordered moments that align along the [1 1 1] direction of the cubic unit cell. We describe the scattering in terms of a two-Gaussian peak fit, which consists of a narrower component that appears below TN≈0.4 K and corresponds to a magnetic correlation length of ξn≈ 80 Å, and a broad component that persists up to T*≈ 0.7 K and corresponds to antiferromagnetic correlations extending over ξb≈ 20 Å. Our results illustrate the fragile magnetic order present in YbBiPt and provide a path forward for microscopic investigations of the ground states and fluctuations associated with the purported quantum critical point in this heavy-fermion compound.

  6. Magnetic properties of nearly stoichiometric CeAuBi{sub 2} heavy fermion compound

    SciTech Connect

    Adriano, C.; Jesus, C. B. R.; Pagliuso, P. G.; Rosa, P. F. S.; Grant, T.; Fisk, Z.; Garcia, D. J.

    2015-05-07

    Motivated by the interesting magnetic anisotropy found in the heavy fermion family CeTX{sub 2} (T = transition metal and X = pnictogen), here, we study the novel parent compound CeAu{sub 1−x}Bi{sub 2−y} by combining magnetization, pressure dependent electrical resistivity, and heat-capacity measurements. The magnetic properties of our nearly stoichiometric single crystal sample of CeAu{sub 1−x}Bi{sub 2−y} (x = 0.92 and y = 1.6) revealed an antiferromagnetic ordering at T{sub N} = 12 K with an easy axis along the c-direction. The field dependent magnetization data at low temperatures reveal the existence of a spin-flop transition when the field is applied along the c-axis (H{sub c} ∼ 7.5 T and T = 5 K). The heat capacity and pressure dependent resistivity data suggest that CeAu{sub 0.92}Bi{sub 1.6} exhibits a weak heavy fermion behavior with strongly localized Ce{sup 3+} 4f electrons. Furthermore, the systematic analysis using a mean field model including anisotropic nearest-neighbors interactions and the tetragonal crystalline electric field (CEF) Hamiltonian allows us to extract a CEF scheme and two different values for the anisotropic J{sub RKKY} exchange parameters between the Ce{sup 3+} ions in this compound. Thus, we discuss a scenario, considering both the anisotropic magnetic interactions and the tetragonal CEF effects, in the CeAu{sub 1−x}Bi{sub 2−y} compounds, and we compare our results with the isostructural compound CeCuBi{sub 2}.

  7. Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn(5).

    PubMed

    Park, W K; Greene, L H

    2009-03-11

    We review the current status of Andreev reflection spectroscopy on the heavy fermions, mostly focusing on the case of CeCoIn(5), a heavy-fermion superconductor with a critical temperature of 2.3 K. This is a well-established technique to investigate superconducting order parameters via measurements of the differential conductance from nanoscale metallic junctions. Andreev reflection is clearly observed in CeCoIn(5) as in other heavy-fermion superconductors. Considering the large mismatch in Fermi velocities, this observation seemingly appears to disagree with the Blonder-Tinkham-Klapwijk (BTK) theory. The measured Andreev signal is highly reduced to the order of maximum ∼13% compared to the theoretically predicted value (100%). The background conductance exhibits a systematic evolution in its asymmetry over a wide temperature range from above the heavy-fermion coherence temperature down to well below the superconducting transition temperature. Analysis of the conductance spectra using the extended BTK model provides a qualitative measure for the superconducting order parameter symmetry, which is determined to be the d(x(2)-y(2)) wave in CeCoIn(5). It is found that existing models do not quantitatively account for the data, which we attribute to the intrinsic properties of the heavy fermions. A substantial body of experimental data and extensive theoretical analysis point to the existence of two-fluid components in CeCoIn(5) and other heavy-fermion compounds. A phenomenological model is proposed employing a Fano interference effect between two conductance channels in order to explain both the conductance asymmetry and the reduced Andreev signal. This model appears plausible not only because it provides good fits to the data but also because it is highly likely that the electrical conduction occurs via two channels, one into the heavy-electron liquid and the other into the conduction electron continuum. Further experimental and theoretical investigations will shed

  8. Optical spectroscopy and ultrafast pump-probe studies on the heavy-fermion compound CePt2In7

    SciTech Connect

    Chen, R. Y.; Zhang, S. J.; Bauer, E. D.; Thompson, J. D.; Wang, N. L.

    2016-07-29

    We report optical spectroscopy and ultrafast pump-probe measurements on the antiferromagnetic heavy-fermion compound CePt 2 In 7 , a member showing stronger two dimensionality than other compounds in the CeIn 3 -derived heavy-fermion family. Here, we identify clear and typical hybridization spectral structures at low temperature from the two different spectroscopy probes. But, the strength and related energy scale of the hybridization are much weaker and smaller than that in the superconducting compounds CeCoIn 5 and CeIrIn 5 . The features are more similar to observations on the antiferromagnetic compounds CeIn 3 and CeRhIn 5 in the same family. Our results clearly indicate that the Kondo interaction and hybridizations exist in the antiferromagnetic compounds but with weaker strength.

  9. Quasi-particle Interference of Heavy Fermions in Resonant X-ray Scattering

    SciTech Connect

    Gyenis, Andras; da Silva Neto, Eduardo H.; Sutarto, Ronny; Schierle, Enrico; He, Feizhou; Weschke, Eugen; Kavai, Mariam; Baumbach, Ryan E.; Thompson, Joe D.; Bauer, Eric D.; Fisk, Zachary; Damascelli, Andrea; Yazdani, Ali; Aynajian, Pegor

    2016-10-14

    Resonant x-ray scattering (RXS) has recently become an increasingly important tool for the study of ordering phenomena in correlated electron systems. Yet, the interpretation of RXS experiments remains theoretically challenging because of the complexity of the RXS cross section. Central to this debate is the recent proposal that impurity-induced Friedel oscillations, akin to quasi-particle interference signals observed with a scanning tunneling microscope (STM), can lead to scattering peaks in RXS experiments. The possibility that quasi-particle properties can be probed in RXS measurements opens up a new avenue to study the bulk band structure of materials with the orbital and element selectivity provided by RXS. We test these ideas by combining RXS and STM measurements of the heavy fermion compound CeMIn5 (M = Co, Rh). Temperature- and doping-dependent RXS measurements at the Ce-M4 edge show a broad scattering enhancement that correlates with the appearance of heavy f-electron bands in these compounds. The scattering enhancement is consistent with the measured quasi-particle interference signal in the STM measurements, indicating that the quasi-particle interference can be probed through the momentum distribution of RXS signals. Overall, our experiments demonstrate new opportunities for studies of correlated electronic systems using the RXS technique.

  10. Renormalization of the periodic Anderson model: An alternative analytical approach to heavy-fermion behavior

    NASA Astrophysics Data System (ADS)

    Hübsch, A.; Becker, K. W.

    2005-04-01

    In this paper a recently developed projector-based renormalization method (PRM) for many-particle Hamiltonians is applied to the periodic Anderson model with the aim to describe heavy-fermion behavior. In this method high-energetic excitation operators instead of high energetic states are eliminated. We arrive at an effective Hamiltonian for a quasifree system which consists of two noninteracting heavy-quasiparticle bands. The resulting renormalization equations for the parameters of the Hamiltonian are valid for large as well as small degeneracy νf of the angular momentum. An expansion in 1/νf is avoided. Within an additional approximation which adapts the idea of a fixed renormalized f level ɛ˜f , we obtain coupled equations for ɛ˜f and the averaged f occupation ⟨nf⟩ . These equations resemble to a certain extent those of the usual slave boson mean-field (SB) treatment. In particular, for large νf the results for the PRM and the SB approach agree perfectly whereas considerable differences are found for small νf .

  11. Spatial interferences in the electron transport of heavy-fermion materials

    NASA Astrophysics Data System (ADS)

    Zhang, Shu-feng; Liu, Yu; Song, Hai-Feng; Yang, Yi-feng

    2016-08-01

    The scanning tunneling microscopy/spectroscopy and the point contact spectroscopy represent major progress in recent heavy-fermion research. Both have revealed important information on the composite nature of the emergent heavy-electron quasiparticles. However, a detailed and thorough microscopic understanding of the similarities and differences in the underlying physical processes of these techniques is still lacking. Here we study the electron transport in the normal state of the periodic Anderson lattice by using the Keldysh nonequilibrium Green's function technique. In addition to the well-known Fano interference between the conduction and f -electron channels, our results further reveal the effect of spatial interference between different spatial paths at the interface on the differential conductance and their interesting interplay with the band features such as the hybridization gap and the Van Hove singularity. We find that the spatial interference leads to a weighted average in the momentum space for the electron transport and could cause suppression of the electronic band features under certain circumstances. In particular, it reduces the capability of probing the f -electron spectral weight near the edges of the hybridization gap for large interface depending on the Fermi surface of the lead. Our results indicate an intrinsic inefficiency of the point contact spectroscopy in probing the f electrons.

  12. Hidden Orbital Order in the Heavy Fermion Metal URu_2Si_2

    NASA Astrophysics Data System (ADS)

    Chandra, Premi

    2003-03-01

    When matter is cooled from high temperatures, collective instabilities develop amongst its constituent particles that lead to new kinds of order. An anomaly in the specific heat, due to a sudden loss of entropy, is a classic signature of this phenomenon. Usually the associated order is easily identified, but sometimes its nature remains elusive. The heavy fermion metal URu_2Si2 is one such example, where the order responsible for the sharp specific heat anomaly at T_0=17 K has remained unidentified despite more than seventeen years of effort. It belongs to a class of ``strongly correlated'' materials where competing interactions lead to correlated electron motion and hence to the possibility of many exotic types of magnetic, charge and superconducting order. The coexistence of large electron-electron repulsion and antiferromagnetic fluctuations in URu_2Si2 leads to an almost incompressible heavy electron fluid, where anisotropically paired quasiparticle states are energetically favored and lead to superconductivity with nodes at 1.5 K. My collaborators(P. Chandra, P. Coleman, J.A. Mydosh and V. Tripathi, Nature, 417, 831 (2002).) and I have developped a detailed proposal for the hidden order in URu_2Si_2. We show that incommensurate orbital antiferromagnetism,associated with circulating currents between the uranium ions, can account for the local fields and entropy loss observed at the 17 K transition; furthermore we make detailed predictions for neutron scattering measurements.

  13. Quasi-particle interference of heavy fermions in resonant x-ray scattering

    PubMed Central

    Gyenis, András; da Silva Neto, Eduardo H.; Sutarto, Ronny; Schierle, Enrico; He, Feizhou; Weschke, Eugen; Kavai, Mariam; Baumbach, Ryan E.; Thompson, Joe D.; Bauer, Eric D.; Fisk, Zachary; Damascelli, Andrea; Yazdani, Ali; Aynajian, Pegor

    2016-01-01

    Resonant x-ray scattering (RXS) has recently become an increasingly important tool for the study of ordering phenomena in correlated electron systems. Yet, the interpretation of RXS experiments remains theoretically challenging because of the complexity of the RXS cross section. Central to this debate is the recent proposal that impurity-induced Friedel oscillations, akin to quasi-particle interference signals observed with a scanning tunneling microscope (STM), can lead to scattering peaks in RXS experiments. The possibility that quasi-particle properties can be probed in RXS measurements opens up a new avenue to study the bulk band structure of materials with the orbital and element selectivity provided by RXS. We test these ideas by combining RXS and STM measurements of the heavy fermion compound CeMIn5 (M = Co, Rh). Temperature- and doping-dependent RXS measurements at the Ce-M4 edge show a broad scattering enhancement that correlates with the appearance of heavy f-electron bands in these compounds. The scattering enhancement is consistent with the measured quasi-particle interference signal in the STM measurements, indicating that the quasi-particle interference can be probed through the momentum distribution of RXS signals. Overall, our experiments demonstrate new opportunities for studies of correlated electronic systems using the RXS technique. PMID:27757422

  14. Coexistence of Antiferromagnetism and Superconductivity in Heavy Fermion Cerium Compound Ce3PdIn11

    PubMed Central

    Kratochvílová, M.; Prokleška, J.; Uhlířová, K.; Tkáč, V.; Dušek, M.; Sechovský, V.; Custers, J.

    2015-01-01

    Many current research efforts in strongly correlated systems focus on the interplay between magnetism and superconductivity. Here we report on coexistence of both cooperative ordered states in recently discovered stoichiometric and fully inversion symmetric heavy fermion compound Ce3PdIn11 at ambient pressure. Thermodynamic and transport measurements reveal two successive magnetic transitions at T1 = 1.67 K and TN = 1.53 K into antiferromagnetic type of ordered states. Below Tc = 0.42 K the compound enters a superconducting state. The large initial slope of dBc2/dT ≈ – 8.6 T/K indicates that heavy quasiparticles form the Cooper pairs. The origin of the two magnetic transitions and the coexistence of magnetism and superconductivity is briefly discussed in the context of the coexistence of the two inequivalent Ce-sublattices in the unit cell of Ce3PdIn11 with different Kondo couplings to the conduction electrons. PMID:26514364

  15. Quasi-particle Interference of Heavy Fermions in Resonant X-ray Scattering

    DOE PAGES

    Gyenis, Andras; da Silva Neto, Eduardo H.; Sutarto, Ronny; ...

    2016-10-14

    Resonant x-ray scattering (RXS) has recently become an increasingly important tool for the study of ordering phenomena in correlated electron systems. Yet, the interpretation of RXS experiments remains theoretically challenging because of the complexity of the RXS cross section. Central to this debate is the recent proposal that impurity-induced Friedel oscillations, akin to quasi-particle interference signals observed with a scanning tunneling microscope (STM), can lead to scattering peaks in RXS experiments. The possibility that quasi-particle properties can be probed in RXS measurements opens up a new avenue to study the bulk band structure of materials with the orbital and elementmore » selectivity provided by RXS. We test these ideas by combining RXS and STM measurements of the heavy fermion compound CeMIn5 (M = Co, Rh). Temperature- and doping-dependent RXS measurements at the Ce-M4 edge show a broad scattering enhancement that correlates with the appearance of heavy f-electron bands in these compounds. The scattering enhancement is consistent with the measured quasi-particle interference signal in the STM measurements, indicating that the quasi-particle interference can be probed through the momentum distribution of RXS signals. Overall, our experiments demonstrate new opportunities for studies of correlated electronic systems using the RXS technique.« less

  16. Coexistence of Antiferromagnetism and Superconductivity in Heavy Fermion Cerium Compound Ce3PdIn11.

    PubMed

    Kratochvílová, M; Prokleška, J; Uhlířová, K; Tkáč, V; Dušek, M; Sechovský, V; Custers, J

    2015-10-30

    Many current research efforts in strongly correlated systems focus on the interplay between magnetism and superconductivity. Here we report on coexistence of both cooperative ordered states in recently discovered stoichiometric and fully inversion symmetric heavy fermion compound Ce3PdIn11 at ambient pressure. Thermodynamic and transport measurements reveal two successive magnetic transitions at T1 = 1.67 K and TN = 1.53 K into antiferromagnetic type of ordered states. Below Tc = 0.42 K the compound enters a superconducting state. The large initial slope of dBc2/dT ≈ - 8.6 T/K indicates that heavy quasiparticles form the Cooper pairs. The origin of the two magnetic transitions and the coexistence of magnetism and superconductivity is briefly discussed in the context of the coexistence of the two inequivalent Ce-sublattices in the unit cell of Ce3PdIn11 with different Kondo couplings to the conduction electrons.

  17. Effect of c-f hybridization on electric and magnetic properties of some Heavy Fermion (HF) systems

    NASA Astrophysics Data System (ADS)

    Sahoo, J.; Nayak, P.

    2017-02-01

    Representing the heavy fermion systems by the Periodic Anderson Model (PAM), we have used Zubarev technique to see the effect of c-f hybridization on the temperature dependence of resistivity and magnetic susceptibility. The calculated resistivity and magnetic susceptibility show the general features observed in these materials experimentally. Further, we have shown how the strength of hybridization as well as the position of the f-level affects both the properties and the Kondo temperature of these systems.

  18. Quest for the Origin of Heavy Fermion Behavior in d-Electron Systems

    NASA Astrophysics Data System (ADS)

    Miyazaki, Masanori; Yamauchi, Ichihiro; Kadono, Ryosuke

    2016-09-01

    Spin fluctuation is presumed to be one of the key properties in understanding the microscopic origin of heavy-fermion-like behavior in the class of transition-metal compounds, including LiV2O4, Y(Sc)Mn2, and YMn2Zn20. In this review, we demonstrate by our recent study of muon spin rotation/relaxation that the temperature (T) dependence of the longitudinal spin relaxation rate (λ ≡ 1/T1) in these compounds exhibits a common trend of leveling off to a constant value (λ ˜ const.) below a characteristic temperature, T*. This is in marked contrast to the behavior predicted for normal metals from the Korringa relation, λ ∝ T/ν, where the spin fluctuation rate (ν) in the Pauli paramagnetic state is given as a constant, ν ≃ 1/[hD(EF)] [with D(EF) being the density of states at the Fermi energy]. Thus, the observed behavior of λ implies that the spin fluctuation rate becomes linearly dependent on temperature, ν ∝ T, suggesting that heavy quasiparticles develop in a manner satisfying D(EF) ∝ (m*)σ ∝ 1/T at lower temperatures (σ determined by the electronic dispersion). Considering that the theory of spin correlation for intersecting Hubbard chains as a model of pyrochlore lattice predicts ν ∝ T, our finding strongly indicates the crucial role of t2g bands which preserve the one-dimensional character at low energies due to the geometrical frustration specific to the undistorted pyrochlore lattice.

  19. Competing magnetic orders in the superconducting state of heavy-fermion CeRhIn5

    DOE PAGES

    Rosa, P. F. S.; Kang, J.; Luo, Yongkang; ...

    2017-05-09

    Applied pressure drives the heavy-fermion antiferromagnet CeRhIn5 toward a quantum critical point that becomes hidden by a dome of unconventional superconductivity. Magnetic fields suppress this superconducting dome, unveiling the quantum phase transition of local character. Here in this paper, we show that 5% magnetic substitution at the Ce site in CeRhIn5, either by Nd or Gd, induces a zero-field magnetic instability inside the superconducting state. This magnetic state not only should have a different ordering vector than the high-field local-moment magnetic state, but it also competes with the latter, suggesting that a spin-density-wave phase is stabilized in zero field bymore » Nd and Gd impurities, similarly to the case of Ce0.95Nd0.05CoIn5. Supported by model calculations, we attribute this spin-density wave instability to a magnetic-impurity-driven condensation of the spin excitons that form inside the unconventional superconducting state.« less

  20. Thermal expansion of the heavy-fermion superconductor PuCoGa5

    NASA Astrophysics Data System (ADS)

    Eloirdi, R.; Giacobbe, C.; Celdran, P. Amador; Magnani, N.; Lander, G. H.; Griveau, J.-C.; Colineau, E.; Miyake, K.; Caciuffo, R.

    2017-03-01

    We have performed high-resolution powder x-ray-diffraction measurements on a sample of PuCoGa2425, the heavy-fermion superconductor with the highest critical temperature of Tc=18.7 K . The results show that the tetragonal symmetry of its crystallographic lattice is preserved down to 2 K. Marginal evidence is obtained for an anomalous behavior below Tc of the a and c lattice parameters. The observed thermal expansion is isotropic down to 150 K and becomes anisotropic for lower temperatures. This gives a c /a ratio that decreases with increasing temperature to become almost constant above ˜150 K . The volume thermal expansion coefficient αV has a jump at Tc, a factor ˜20 larger than the change predicted by the Ehrenfest relation for a second-order phase transition. The volume expansion deviates from the curve expected for the conventional anharmonic behavior described by a simple Grüneisen-Einstein model. The observed differences are about ten times larger than the statistical error bars but are too small to be taken as an indication for the proximity of the system to a valence instability that is avoided by the superconducting state.

  1. Quantum bicriticality in the heavy-fermion metamagnet YbAgGe.

    PubMed

    Tokiwa, Y; Garst, M; Gegenwart, P; Bud'ko, S L; Canfield, P C

    2013-09-13

    Bicritical points, at which two distinct symmetry-broken phases become simultaneously unstable, are typical for spin-flop metamagnetism. Interestingly, the heavy-fermion compound YbAgGe also possesses such a bicritical point (BCP) with a low temperature T(BCP)≈0.3  K at a magnetic field of μH(BCP)≈4.5  T. In its vicinity, YbAgGe exhibits anomalous behavior that we attribute to the influence of a quantum bicritical point that is close in parameter space yet can be reached by tuning T(BCP) further to zero. Using high-resolution measurements of the magnetocaloric effect, we demonstrate that the magnetic Grüneisen parameter ΓH indeed both changes sign and diverges as required for quantum criticality. Moreover, ΓH displays a characteristic scaling behavior but only on the low-field side H≲H(BCP), indicating a pronounced asymmetry with respect to the critical field. We speculate that the small value of T(BCP) is related to the geometric frustration of the Kondo lattice of YbAgGe.

  2. Quantum Bicriticality in the Heavy-Fermion Metamagnet YbAgGe

    NASA Astrophysics Data System (ADS)

    Tokiwa, Y.; Garst, M.; Gegenwart, P.; Bud'ko, S. L.; Canfield, P. C.

    2013-09-01

    Bicritical points, at which two distinct symmetry-broken phases become simultaneously unstable, are typical for spin-flop metamagnetism. Interestingly, the heavy-fermion compound YbAgGe also possesses such a bicritical point (BCP) with a low temperature TBCP≈0.3K at a magnetic field of μ0HBCP≈4.5T. In its vicinity, YbAgGe exhibits anomalous behavior that we attribute to the influence of a quantum bicritical point that is close in parameter space yet can be reached by tuning TBCP further to zero. Using high-resolution measurements of the magnetocaloric effect, we demonstrate that the magnetic Grüneisen parameter ΓH indeed both changes sign and diverges as required for quantum criticality. Moreover, ΓH displays a characteristic scaling behavior but only on the low-field side H≲HBCP, indicating a pronounced asymmetry with respect to the critical field. We speculate that the small value of TBCP is related to the geometric frustration of the Kondo lattice of YbAgGe.

  3. Competing magnetic orders in the superconducting state of heavy-fermion CeRhIn5

    NASA Astrophysics Data System (ADS)

    Rosa, P. F. S.; Kang, J.; Luo, Yongkang; Wakeham, N.; Bauer, E. D.; Ronning, F.; Fisk, Z.; Fernandes, R. M.; Thompson, J. D.

    2017-05-01

    Applied pressure drives the heavy-fermion antiferromagnet CeRhIn5 toward a quantum critical point that becomes hidden by a dome of unconventional superconductivity. Magnetic fields suppress this superconducting dome, unveiling the quantum phase transition of local character. Here, we show that 5%5% magnetic substitution at the Ce site in CeRhIn5, either by Nd or Gd, induces a zero-field magnetic instability inside the superconducting state. This magnetic state not only should have a different ordering vector than the high-field local-moment magnetic state, but it also competes with the latter, suggesting that a spin-density-wave phase is stabilized in zero field by Nd and Gd impurities, similarly to the case of Ce0.95Nd0.05CoIn5. Supported by model calculations, we attribute this spin-density wave instability to a magnetic-impurity-driven condensation of the spin excitons that form inside the unconventional superconducting state.

  4. Correlation between ground state and orbital anisotropy in heavy fermion materials

    DOE PAGES

    Willers, Thomas; Strigari, Fabio; Hu, Zhiwei; ...

    2015-02-09

    The interplay of structural, orbital, charge, and spin degrees of freedom is at the heart of many emergent phenomena, including superconductivity. We find that unraveling the underlying forces of such novel phases is a great challenge because it not only requires understanding each of these degrees of freedom, it also involves accounting for the interplay between them. Cerium-based heavy fermion compounds are an ideal playground for investigating these interdependencies, and we present evidence for a correlation between orbital anisotropy and the ground states in a representative family of materials. We have measured the 4f crystal-electric field ground-state wave functions ofmore » the strongly correlated materials CeRh1₋xIrxIn5 with great accuracy using linear polarization-dependent soft X-ray absorption spectroscopy. These measurements show that these wave functions correlate with the ground-state properties of the substitution series, which covers long-range antiferromagnetic order, unconventional superconductivity, and coexistence of these two states.« less

  5. Pairing Symmetry of Heavy Fermion Superconductivity in the Two-Dimensional Kondo—Heisenberg Lattice Model

    NASA Astrophysics Data System (ADS)

    Liu, Yu; Zhang, Guang-Ming; Yu, Lu

    2014-08-01

    In the two-dimensional Kondo—Heisenberg lattice model away from half-filled, the local antiferromagnetic exchange coupling can provide the pairing mechanism of quasiparticles via the Kondo screening effect, leading to the heavy fermion superconductivity. We find that the pairing symmetry strongly depends on the Fermi surface (FS) structure in the normal metallic state. When JH/JK is very small, the FS is a small hole-like circle around the corner of the Brillouin zone, and the s-wave pairing symmetry has a lower ground state energy. For the intermediate coupling values of JH/JK, the extended s-wave pairing symmetry gives the favored ground state. However, when JH/JK is larger than a critical value, the FS transforms into four small hole pockets crossing the boundary of the magnetic Brillouin zone, and the d-wave pairing symmetry becomes more favorable. In that regime, the resulting superconducting state is characterized by either a nodal d-wave or nodeless d-wave state, depending on the conduction electron filling factor as well. A continuous phase transition exists between these two states. This result may be related to the phase transition of the nodal d-wave state to a fully gapped state, which has recently been observed in Yb-doped CeCoIn5.

  6. Unconventional Pairing States in Heavy-Fermion Superconductors Studied by the NQR/NMR Experiments

    NASA Astrophysics Data System (ADS)

    Kitaoka, Yoshio; Mukuda, Hidekazu; Yashima, Mitsuharu; Harada, Atsushi

    2007-05-01

    We review the studies on the unconventional superconducting pairing states and their relevance with magnetism in the f-electron derived heavy-fermion (HF) systems by means of nuclear-magnetic-resonance (NMR) and nuclear-quadrupole-resonance (NQR). These studies have unraveled a rich variety of the phenomena in the ground state of HF systems. In this article, we address an intimate relationship between the onset of strong-coupling superconductivity (SC) and critical magnetic fluctuations emerging in the vicinity of quantum critical point (QCP). Furthermore, we focus on the novel phase diagram of the HF antiferromagnet CeRhIn5 under pressure which is characterized by the tetracritical point separating the pure antiferromagnetism (AFM) phase, the AFM+SC uniformly coexisting phase, and the paramagnetic SC phase. A comparison is also presented on the AFM+SC uniformly coexisting phase in high-temperature superconductors as the function of carrier doping. As a consequence, we raise a question; Do we need a bosonic glue to pair electrons in these superconductors? Finally, we address a possible origin of the novel SC in the itinerant ferromagnet UGe2, which is mediated by ferromagnetic spin-density fluctuations relevant with the first-order transition inside the ferromagnetic states.

  7. Kondo lattice heavy fermion behavior in CeRh2Ga2

    NASA Astrophysics Data System (ADS)

    Anand, V. K.; Adroja, D. T.; Bhattacharyya, A.; Klemke, B.; Lake, B.

    2017-04-01

    The physical properties of an intermetallic compound CeRh2Ga2 have been investigated by magnetic susceptibility χ (T) , isothermal magnetization M(H), heat capacity {{C}\\text{p}}(T) , electrical resistivity ρ (T) , thermal conductivity κ (T) and thermopower S(T) measurements. CeRh2Ga2 is found to crystallize with CaBe2Ge2-type primitive tetragonal structure (space group P4/nmm). No evidence of long range magnetic order is seen down to 1.8 K. The χ (T) data show paramagnetic behavior with an effective moment {μ\\text{eff}}≈ 2.5~{μ\\text{B}} /Ce indicating Ce3+ valence state of Ce ions. The ρ (T) data exhibit Kondo lattice behavior with a metallic ground state. The low-T {{C}\\text{p}}(T) data yield an enhanced Sommerfeld coefficient γ =130(2) mJ/mol K2 characterizing CeRh2Ga2 as a moderate heavy fermion system. The high-T {{C}\\text{p}}(T) and ρ (T) show an anomaly near 255 K, reflecting a phase transition. The κ (T) suggests phonon dominated thermal transport with considerably higher values of Lorenz number L(T) compared to the theoretical Sommerfeld value L 0.

  8. Heavy fermions, quantum criticality, and unconventional superconductivity in filled skutterudites and related materials

    SciTech Connect

    Andraka, Bohdan

    2015-05-14

    The main goal of this program was to explore the possibility of novel states and behaviors in Pr-based system exhibiting quantum critical behavior, PrOs₄Sb₁₂. Upon small changes of external parameter, such as magnetic field, physical properties of PrOs₄Sb₁₂ are drastically altered from those corresponding to a superconductor, to heavy fermion, to field-induced ordered phase with primary quadrupolar order parameter. All these states are highly unconventional and not understood in terms of current theories thus offer an opportunity to expand our knowledge and understanding of condensed matter. At the same time, these novel states and behaviors are subjects to intense international controversies. In particular, two superconducting phases with different transition temperatures were observed in some samples and not observed in others leading to speculations that sample defects might be partially responsible for these exotic behaviors. This work clearly established that crystal disorder is important consideration, but contrary to current consensus this disorder suppresses exotic behavior. Superconducting properties imply unconventional inhomogeneous state that emerges from unconventional homogeneous normal state. Comprehensive structural investigations demonstrated that upper superconducting transition is intrinsic, bulk, and unconventional. The high quality of in-house synthesized single crystals was indirectly confirmed by de Haas-van Alphen quantum oscillation measurements. These measurements, for the first time ever reported, spanned several different phases, offering unprecedented possibility of studying quantum oscillations across phase boundaries.

  9. Non-universal bound states of two identical heavy fermions and one light particle

    NASA Astrophysics Data System (ADS)

    Safavi, Arghavan; Rittenhouse, Seth; Blume, Dorte; Sadeghpour, Hossein

    2013-05-01

    We study a system of two identical heavy fermions of mass M and light particle of mass m. The interspecies interaction is modeled using a short-range two-body potential with positive s-wave scattering length. We impose a short-range boundary condition on the logarithmic derivative of the hyperradial wavefunction and show that, in the regime where Efimov states are absent, a non-universal three-body state ``cuts through'' the universal three-body states previously described by Kartavtsev and Malykh [O. I. Kartavtsev and A. V. Malykh, J. Phys. B 40, 1429 (2007)]. We study the effect of the non-universal state on the behavior of the universal states and use a simple quantum defect theory, utilizing hyperspherical coordinates, to explain the existence of the non-universal state. An empirical two-state model is employed to quantify the coupling of the non-universal state to the universal states. This work was supported by NSF through a grant for the Institute for Theoretical Atomic, Molecular and Optical Physics at Harvard University and Smithsonian Astrophysical Observatory and through grant PHY-1205443.

  10. Kondo lattice heavy fermion behavior in CeRh2Ga2.

    PubMed

    Anand, V K; Adroja, D T; Bhattacharyya, A; Klemke, B; Lake, B

    2017-04-05

    The physical properties of an intermetallic compound CeRh2Ga2 have been investigated by magnetic susceptibility [Formula: see text], isothermal magnetization M(H), heat capacity [Formula: see text], electrical resistivity [Formula: see text], thermal conductivity [Formula: see text] and thermopower S(T) measurements. CeRh2Ga2 is found to crystallize with CaBe2Ge2-type primitive tetragonal structure (space group P4/nmm). No evidence of long range magnetic order is seen down to 1.8 K. The [Formula: see text] data show paramagnetic behavior with an effective moment [Formula: see text]/Ce indicating Ce(3+) valence state of Ce ions. The [Formula: see text] data exhibit Kondo lattice behavior with a metallic ground state. The low-T [Formula: see text] data yield an enhanced Sommerfeld coefficient [Formula: see text] mJ/mol K(2) characterizing CeRh2Ga2 as a moderate heavy fermion system. The high-T [Formula: see text] and [Formula: see text] show an anomaly near 255 K, reflecting a phase transition. The [Formula: see text] suggests phonon dominated thermal transport with considerably higher values of Lorenz number L(T) compared to the theoretical Sommerfeld value L 0.

  11. Sb-NMR/NQR studies of heavy fermion system YbRhSb

    NASA Astrophysics Data System (ADS)

    Kishimoto, Yasuki; Awai, Yosiki; Kotegawa, Hisashi; Tou, Hideki; Muro, Yuji; Nakamura, Koji; Sera, Masafumi; Takabatake, Toshiro

    2017-04-01

    We report a study of 121Sb nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) in a Yb-based heavy fermion system YbRhSb using a single crystal. Sharp 121Sb-NMR lines were observed for each crystal axis for B‖a,b,c. From comparison with observed Sb-NMR spectra and numerical simulations, electric field gradient (EFG) parameters and Knight shift parameters are obtained at 10 K. The obtained quadrupole frequency, asymmetry parameter, isotropic Knight shift and anisotropic principal values of Knight shift tensors are νQ = 18.8 MHz, η =0.2,\\text{\\hspace{0.17em}}{K}{iso}≈ 0.6 % , and ({K}\\text{ax}x,{K}\\text{ax}y,{K}\\text{ax}z)≈ (-3.5,4.1,-0.6) % , respectively. We also succeeded in observing 121Sb-NQR signals at around 19.5 and 37 MHz, which are reproduced by the nuclear quadrupole Hamiltonian with νQ = 18.8 MHz and η = 0.2. We mention the relation between the anisotropy of the Knight shift and magnetic susceptibility. Our NMR/NQR results suggest that the weak ferromagnetism in YbRhSb is ascribed to a canted antiferromagnetic state.

  12. Magnetic-field-tuned quantum criticality of the heavy-fermion system YbPtBi

    SciTech Connect

    Mun, E. D.; Budko, Serguei L.; Martin, Catalin; Kim, Hyong June; Tanatar, Makariy A.; Park, J.-H.; Murphy, T.; Schmiedeshoff, G. M.; Dilley, N.; Prozorov, Ruslan; Canfield, Paul C.

    2013-02-15

    In this paper, we present systematic measurements of the temperature and magnetic field dependencies of the thermodynamic and transport properties of the Yb-based heavy fermion YbPtBi for temperatures down to 0.02 K with magnetic fields up to 140 kOe to address the possible existence of a field-tuned quantum critical point. Measurements of magnetic-field- and temperature-dependent resistivity, specific heat, thermal expansion, Hall effect, and thermoelectric power indicate that the AFM order can be suppressed by an applied magnetic field of Hc~4 kOe. In the H-T phase diagram of YbPtBi, three regimes of its low-temperature states emerge: (I) AFM state, characterized by a spin density wave-like feature, which can be suppressed to T=0 by the relatively small magnetic field of Hc~4 kOe; (II) field-induced anomalous state in which the electrical resistivity follows Δρ(T)∝T1.5 between Hc and ~8 kOe; and (III) Fermi liquid (FL) state in which Δρ(T)∝T2 for H≥8 kOe. Regions I and II are separated at T=0 by what appears to be a quantum critical point. Whereas region III appears to be a FL associated with the hybridized 4f states of Yb, region II may be a manifestation of a spin liquid state.

  13. Complex magnetic phases in non-centrosymmetric heavy fermion CeCoGe3

    NASA Astrophysics Data System (ADS)

    Wu, Shan; Stock, Chris; Petrovic, Cedomir; Rodriguez-Rivera, J. A.; Broholm, Collin

    The non-centrosymmetric nature of the tetragonal heavy fermion system CeCoGe3 has attracted much interest in the high pressure superconducting state of the material. We have explored the related ambient pressure magnetism using neutron scattering. There are three successive phase transitions at TN 1 ~ 21 K , TN 2 ~ 12 K and TN 3 ~ 8 K. The upper transition greatly enhances the susceptibility and there are meta-magnetic transitions in the lower T phases. We confirmed the previously determined AFM spin structure for TN 2 < T

  14. Heavy fermion and Kondo lattice behavior in the itinerant ferromagnet CeCrGe3.

    PubMed

    Das, Debarchan; Gruner, T; Pfau, H; Paramanik, U B; Burkhardt, U; Geibel, C; Hossain, Z

    2014-03-12

    Physical properties of polycrystalline CeCrGe3 and LaCrGe3 have been investigated by x-ray absorption spectroscopy, magnetic susceptibility χ(T), isothermal magnetization M(H), electrical resistivity ρ(T), specific heat C(T) and thermoelectric power S(T) measurements. These compounds are found to crystallize in the hexagonal perovskite structure (space group P63/mmc), as previously reported. The ρ(T), χ(T) and C(T) data confirm the bulk ferromagnetic ordering of itinerant Cr moments in LaCrGe3 and CeCrGe3 with TC = 90 K and 70 K respectively. In addition, a weak anomaly is also observed near 3 K in the C(T) data of CeCrGe3. The T dependences of ρ and finite values of Sommerfeld coefficient γ obtained from the specific heat measurements confirm that both the compounds are of metallic character. Further, the T dependence of ρ of CeCrGe3 reflects a Kondo lattice behavior. An enhanced γ of 130 mJ mol(-1) K(-2) together with the Kondo lattice behavior inferred from the ρ(T) establish CeCrGe3 as a moderate heavy fermion compound with a quasi-particle mass renormalization factor of ∼45.

  15. Field-induced density wave in the heavy-fermion compound CeRhIn₅.

    PubMed

    Moll, Philip J W; Zeng, Bin; Balicas, Luis; Galeski, Stanislaw; Balakirev, Fedor F; Bauer, Eric D; Ronning, Filip

    2015-03-23

    Strong electron correlations lead to a variety of distinct ground states, such as magnetism, charge order or superconductivity. Understanding the competitive or cooperative interplay between neighbouring phases is an outstanding challenge in physics. CeRhIn₅ is a prototypical example of a heavy-fermion superconductor: it orders anti-ferromagnetically below 3.8 K, and moderate hydrostatic pressure suppresses the anti-ferromagnetic order inducing unconventional superconductivity. Here we show evidence for a phase transition to a state akin to a density wave (DW) under high magnetic fields (>27 T) in high-quality single crystal microstructures of CeRhIn₅. The DW is signalled by a hysteretic anomaly in the in-plane resistivity accompanied by non-linear electrical transport, yet remarkably thermodynamic measurements suggest that the phase transition involves only small portions of the Fermi surface. Such a subtle order might be a common feature among correlated electron systems, reminiscent of the similarly subtle charge DW state in the cuprates.

  16. Correlation between ground state and orbital anisotropy in heavy fermion materials.

    PubMed

    Willers, Thomas; Strigari, Fabio; Hu, Zhiwei; Sessi, Violetta; Brookes, Nicholas B; Bauer, Eric D; Sarrao, John L; Thompson, J D; Tanaka, Arata; Wirth, Steffen; Tjeng, Liu Hao; Severing, Andrea

    2015-02-24

    The interplay of structural, orbital, charge, and spin degrees of freedom is at the heart of many emergent phenomena, including superconductivity. Unraveling the underlying forces of such novel phases is a great challenge because it not only requires understanding each of these degrees of freedom, it also involves accounting for the interplay between them. Cerium-based heavy fermion compounds are an ideal playground for investigating these interdependencies, and we present evidence for a correlation between orbital anisotropy and the ground states in a representative family of materials. We have measured the 4f crystal-electric field ground-state wave functions of the strongly correlated materials CeRh1-xIrxIn5 with great accuracy using linear polarization-dependent soft X-ray absorption spectroscopy. These measurements show that these wave functions correlate with the ground-state properties of the substitution series, which covers long-range antiferromagnetic order, unconventional superconductivity, and coexistence of these two states.

  17. Heavy Dirac fermions in a graphene/topological insulator hetero-junction

    NASA Astrophysics Data System (ADS)

    Cao, Wendong; Zhang, Rui-Xing; Tang, Peizhe; Yang, Gang; Sofo, Jorge; Duan, Wenhui; Liu, Chao-Xing

    2016-09-01

    The low energy physics of both graphene and surface states of three-dimensional topological insulators (TIs) is described by gapless Dirac fermions with linear dispersion. In this work, we predict the emergence of a ‘heavy’ Dirac fermion in a graphene/TI hetero-junction, where the linear term almost vanishes and the corresponding energy dispersion becomes highly nonlinear. By combining ab initio calculations and an effective low-energy model, we show explicitly how strong hybridization between Dirac fermions in graphene and the surface states of TIs can reduce the Fermi velocity of Dirac fermions. Due to the negligible linear term, interaction effects will be greatly enhanced and can drive ‘heavy’ Dirac fermion states into the half quantum Hall state with non-zero Hall conductance.

  18. Electronic Structure of Heavy Fermion Uranium Compounds Studied by Core-Level Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Fujimori, Shin-ichi; Ohkochi, Takuo; Kawasaki, Ikuto; Yasui, Akira; Takeda, Yukiharu; Okane, Tetsuo; Saitoh, Yuji; Fujimori, Atsushi; Yamagami, Hiroshi; Haga, Yoshinori; Yamamoto, Etsuji; Tokiwa, Yoshifumi; Ikeda, Shugo; Sugai, Takashi; Ohkuni, Hitoshi; Kimura, Noriaki; Ōnuki, Yoshichika

    2012-01-01

    High-energy-resolution core-level and valence-band photoelectron spectroscopic studies were performed for the heavy fermion uranium compounds UGe2, UCoGe, URhGe, URu2Si2, UNi2Al3, UPd2Al3, and UPt3 as well as typical localized and itinerant uranium compounds to understand the relationship between the uranium valence state and their core-level spectral line shapes. In addition to the main line and high-binding energy satellite structure recognized in the core-level spectra of uranium compounds, a shoulder structure on the lower binding energy side of the main lines of localized and nearly localized uranium compounds was also found. The spectral line shapes show a systematic variation depending on the U 5f electronic structure. The core-level spectra of UGe2, UCoGe, URhGe, URu2Si2, and UNi2Al3 are rather similar to those of itinerant compounds, suggesting that U 5f electrons in these compounds are well hybridized with ligand states. On the other hand, the core-level spectra of UPd2Al3 and UPt3 show considerably different spectral line shapes from those of the itinerant compounds, suggesting that U 5f electrons in UPd2Al3 and UPt3 are less hybridized with ligand states, leading to the correlated nature of U 5f electrons in these compounds. The dominant final state characters in their core-level spectra suggest that the numbers of 5f electrons in UGe2, UCoGe, URhGe, URu2Si2, UNi2Al3, and UPd2Al3 are close to but less than three, while that of UPt3 is close to two rather than to three.

  19. Landau Renormalizations of Superfluid Density in the Heavy-Fermion Superconductor CeCoIn5

    NASA Astrophysics Data System (ADS)

    Shu, Lei; Maclaughlin, D. E.; Varma, C. M.; Bernal, O. O.; Ho, P.-C.; Fukuda, R. H.; Shen, X. P.; Maple, M. B.

    2015-03-01

    The formation of heavy fermion (HF) bands can occur by means of the conversion of a periodic array of local moments into itinerant electrons via the Kondo effect and the huge consequent Fermi-liquid(FL) renormalizations. Leggett predicted for liquid 3He that FL renormalizations change in the superconducting state, leading to a temperature(T) dependence of the London penetration depth Λ quite different from that in the BCS theory. Using Leggett's theory, as modified for HF, it is possible to extract from the measured T dependence of Λ in high quality samples both Landau parameters F0s and F1s; this has never been accomplished before. A modification of the T dependence of the specific heat Cel, related to that of Λ, is also expected. We have carefully determined the magnitude and T dependence of Λ in CeCoIn5 by muon spin relaxation rate measurements to obtain F0s = 36 +/- 1 and F1s = 1 . 2 +/- 0 . 3 , and find a consistent change in the T dependence of electronic specific heat Cel. This, the first determination of F1s with a value <

  20. Hybridization and superconducting gaps in heavy-fermion superconductor PuCoGa5 probed via the dynamics of photoinduced quasiparticles

    SciTech Connect

    Talbayev, Diyar; Trugman, Stuart A; Zhu, Jian - Xin; Bauer, Eric D; Kennison, John A; Mitchell, Jeremy N; Thompson, Joe D; Sarrao, John L; Taylor, Antoinette J; Burch, Kenneth S; Chia, Elbert E. M.

    2009-01-01

    We have examined the relaxation of photoinduced quasiparticles in the heavy-fermion superconductor PuCoGa{sub 5}. The deduced electron-phonon coupling constant is incompatible with the measured superconducting transition temperature T{sub c}, which speaks against phonon-mediated superconducting pairing. Upon lowering the temperature, we observe an order-of-magnitude increase of the quasiparticle relaxation time in agreement with the phonon bottleneck scenario - evidence for the presence of a hybridization gap in the electronic density of states. The modification of photoinduced reflectance in the superconducting state is consistent with the heavy character of the quasiparticles that participate in Cooper pairing. The discovery of relatively high-temperature superconductivity in the Pu-based compounds PuCoGa{sub 5} (T{sub c} = 18.5 K) and PuRhGa{sub 5} (T{sub c} = 8.7 K) has renewed the interest in actinide materials research. The Pu-based superconductors share the HoCoGa{sub 5}-type tetragonal lattice stucture with the Ce-based series of compounds (CeRhIn{sub 5}, CeCoIn{sub 5}, and CeIrIn{sub 5}) commonly referred to as '115' materials. In the Ce-based 115 compounds, CeIrIn{sub 5} (T{sub c} = 0.4 K) and CeCoIn{sub 5} (T{sub c} = 2.3 K), display superconductivity at ambient pressure. Both Ce- and Pu-based 115 compounds display the heavy fermion behavior resulting from the influence of 4f (Ce) and 5f (Pu) electrons. The most intriguing question concerns the origin of superconductivity (SC) in the 115 materials. In the Ce series, the d-wave symmetry of the SC order parameter and the proximity of SC order to magnetism have lead to a widespread belief that the unconventional SC is induced by antiferromagnetic spin fluctuations. In the Pu compounds, two possible scenarios regarding the SC mechanism have been considered: one approach favors a magnetically mediated unconventional SC similar to that in CeCoIn{sub 5}. In the other scenario, the conventional SC is mediated by

  1. Direct evidence for a magnetic f-electron-mediated pairing mechanism of heavy-fermion superconductivity in CeCoIn5.

    PubMed

    Van Dyke, John S; Massee, Freek; Allan, Milan P; Davis, J C Séamus; Petrovic, Cedomir; Morr, Dirk K

    2014-08-12

    To identify the microscopic mechanism of heavy-fermion Cooper pairing is an unresolved challenge in quantum matter studies; it may also relate closely to finding the pairing mechanism of high-temperature superconductivity. Magnetically mediated Cooper pairing has long been the conjectured basis of heavy-fermion superconductivity but no direct verification of this hypothesis was achievable. Here, we use a novel approach based on precision measurements of the heavy-fermion band structure using quasiparticle interference imaging to reveal quantitatively the momentum space (k-space) structure of the f-electron magnetic interactions of CeCoIn5. Then, by solving the superconducting gap equations on the two heavy-fermion bands Ek(α,β) with these magnetic interactions as mediators of the Cooper pairing, we derive a series of quantitative predictions about the superconductive state. The agreement found between these diverse predictions and the measured characteristics of superconducting CeCoIn5 then provides direct evidence that the heavy-fermion Cooper pairing is indeed mediated by f-electron magnetism.

  2. Direct evidence for a magnetic f-electron–mediated pairing mechanism of heavy-fermion superconductivity in CeCoIn5

    PubMed Central

    Van Dyke, John S.; Massee, Freek; Allan, Milan P.; Davis, J. C. Séamus; Petrovic, Cedomir; Morr, Dirk K.

    2014-01-01

    To identify the microscopic mechanism of heavy-fermion Cooper pairing is an unresolved challenge in quantum matter studies; it may also relate closely to finding the pairing mechanism of high-temperature superconductivity. Magnetically mediated Cooper pairing has long been the conjectured basis of heavy-fermion superconductivity but no direct verification of this hypothesis was achievable. Here, we use a novel approach based on precision measurements of the heavy-fermion band structure using quasiparticle interference imaging to reveal quantitatively the momentum space (k-space) structure of the f-electron magnetic interactions of CeCoIn5. Then, by solving the superconducting gap equations on the two heavy-fermion bands Ekα,β with these magnetic interactions as mediators of the Cooper pairing, we derive a series of quantitative predictions about the superconductive state. The agreement found between these diverse predictions and the measured characteristics of superconducting CeCoIn5 then provides direct evidence that the heavy-fermion Cooper pairing is indeed mediated by f-electron magnetism. PMID:25062692

  3. A new ternary magnetically ordered heavy fermion compound Pr2Rh3Ge: magnetic, electronic and thermodynamic properties.

    PubMed

    Falkowski, M; Strydom, A M

    2017-10-04

    The results of the magnetic, electron transport, heat capacity and heat conduction measurements on the new rhombohedral ternary compound Pr2Rh3Ge have been investigated. The synthesized polycrystalline compound was found to crystallize in the ternary ordered variant of the cubic Laves phase [Formula: see text]-type of structure with the space group R[Formula: see text]m, as previously reported. Pr2Rh3Ge exhibits a ferromagnetic behaviour below [Formula: see text] K, which was found to be unstable in low applied magnetic fields, revealing characteristics usually attributed to the long-range order. In the entire paramagnetic region electrical resistivity shows monotonous metallic conductivity character. We estimated that the Sommerfeld coefficient γ  =  315 mJ/Pr-mol · [Formula: see text] of [Formula: see text] [Formula: see text]Ge is very large with comparison to ordinary metals which indicate the existence of heavy fermion behaviour of itinerant charge carriers at low temperatures or enhanced density of the quasi-particle state at the Fermi level. The crucial role of the crystalline electric field effects on the ground state properties of [Formula: see text] (J  =  4) has been also observed. We think that the heavy fermion behaviour in [Formula: see text] [Formula: see text]Ge results from the dynamic low-lying crystal-field fluctuations, since there is no sign of Kondo effect in electrical resistivity and no enhancement of the slope S(T)/T in thermoelectric power data at low temperatures. It suggests that the conduction electrons at the Fermi level does not correlate with the 4f (2) states of [Formula: see text] atoms and hence there is no place for a typical spin Kondo effect, as it is commonly observed in Ce- and Yb-based heavy fermion systems.

  4. A new ternary magnetically ordered heavy fermion compound Pr2Rh3Ge: magnetic, electronic and thermodynamic properties

    NASA Astrophysics Data System (ADS)

    Falkowski, M.; Strydom, A. M.

    2017-10-01

    The results of the magnetic, electron transport, heat capacity and heat conduction measurements on the new rhombohedral ternary compound Pr2Rh3Ge have been investigated. The synthesized polycrystalline compound was found to crystallize in the ternary ordered variant of the cubic Laves phase MgCu2 -type of structure with the space group R\\overline{3} m, as previously reported. Pr2Rh3Ge exhibits a ferromagnetic behaviour below TC = 8.5 K, which was found to be unstable in low applied magnetic fields, revealing characteristics usually attributed to the long-range order. In the entire paramagnetic region electrical resistivity shows monotonous metallic conductivity character. We estimated that the Sommerfeld coefficient γ  =  315 mJ/Pr-mol · K2 of Pr2 Rh3 Ge is very large with comparison to ordinary metals which indicate the existence of heavy fermion behaviour of itinerant charge carriers at low temperatures or enhanced density of the quasi-particle state at the Fermi level. The crucial role of the crystalline electric field effects on the ground state properties of Pr3+ (J  =  4) has been also observed. We think that the heavy fermion behaviour in Pr2 Rh3 Ge results from the dynamic low-lying crystal-field fluctuations, since there is no sign of Kondo effect in electrical resistivity and no enhancement of the slope S(T)/T in thermoelectric power data at low temperatures. It suggests that the conduction electrons at the Fermi level does not correlate with the 4f 2 states of Pr3+ atoms and hence there is no place for a typical spin Kondo effect, as it is commonly observed in Ce- and Yb-based heavy fermion systems.

  5. Charm spectroscopy on dynamical 2+1 flavor domain wall fermion lattices with a relativistic heavy quark action

    SciTech Connect

    Min Li; Huey-Wen Lin

    2007-10-01

    We present a preliminary calculation of the charmonium spectrum using the dynamical 2+1 flavor $24^3\\times 64$ domain wall fermion lattice configurations generated by the RBC and UKQCD collaborations. We use the relativistic heavy quark action with 3 parameters non-perturbatively determined by matching to experimental quantities. Chiral extrapolation is done on four light sea quark masses from 0.005 to 0.03, with $m_s=0.04$ and $m_{res}=0.003$. We can either predict meson masses assuming the lattice spacing is known from other methods, or calculate the lattice spacing using those quantities.

  6. Low-temperature specific heat of the heavy-fermion superconductor PrOs4Sb12.

    PubMed

    Vollmer, R; Faisst, A; Pfleiderer, C; V Löhneysen, H; Bauer, E D; Ho, P-C; Zapf, V; Maple, M B

    2003-02-07

    We report the magnetic field dependence of the specific-heat C of single crystals of the first Pr-based heavy-fermion superconductor Pr(Os4Sb12. The variation of C at low temperature and the magnetic phase diagram inferred from C, the resistivity and magnetization provide compelling evidence of a doublet ground state. Two distinct superconducting anomalies in C indicate an unconventional superconducting state, where the splitting may arise from a weak lifting of the ground state degeneracy. In combination this identifies Pr(Os4Sb12 as a strong contender for quadrupolar pairing, i.e., superconductivity that is neither electron-phonon nor magnetically mediated.

  7. Theory of the electron spin resonance in the heavy fermion metal β-YbAlB4.

    PubMed

    Ramires, Aline; Coleman, Piers

    2014-03-21

    The heavy fermion metal β-YbAlB4 exhibits a bulk room temperature conduction electron spin resonance (ESR) signal which evolves into an Ising-anisotropic f-electron signal exhibiting hyperfine features at low temperatures. We develop a theory for this phenomenon based on the development of resonant scattering off a periodic array of Kondo centers. We show that the hyperfine structure arises from the scattering off the Yb atoms with nonzero nuclear spin, while the constancy of the ESR intensity is a consequence of the presence of crystal electric field excitations of the order of the hybridization strength.

  8. An algebraic fermion description of band termination and loss of collectivity in heavy nuclei

    NASA Astrophysics Data System (ADS)

    Guidry, Mike W.; Wu, Cheng-Li; Li, Zhen-Ping; Feng, Da Hsuan; Ginocchio, Joseph N.

    1987-03-01

    An algebraic fermion model is used to interpret the loss of E2 collectivity observed in two- and four-quasiparticle aligned bands, and the termination of collective bands at high spins in rare-earth nuclei. Both can be understood as a systematic consequence of finite angular momentum content in a coherent SU 3 core.

  9. Modified top quark condensation model with the extra heavy fermion, the 125 GeV pseudo-Goldstone boson, and the additional heavy scalar bosons

    NASA Astrophysics Data System (ADS)

    Khaidukov, Z. V.; Zubkov, M. A.

    2017-08-01

    We discuss the modified top quark condensation model proposed in Ref. 54. This construction was inspired by the top-seesaw scenario, in which the extra heavy fermion χ that may be paired with the top quark is added. Besides, this model incorporates the ideas of the little Higgs scenario, in which the 125 GeV scalar particle appears as a pseudo-Goldstone boson. This model admits (in addition to the 125 GeV scalar boson H) the heavier scalar excitation H‧. We consider the region of parameters, where its mass is MH‧˜ 1TeV, the width of H‧ is ΓH‧˜ 0.3MH‧, while the mass of the heavy fermion is mχ ˜ 1TeV. We find that in this model the value of the cross-section σpp→H‧+X→γ+γ+X for s = 13TeV is essentially smaller than the present experimental upper bound. Besides, we find that for the chosen values of parameters there should exist the CP-even scalar boson with mass ≈ 2mχ and very small width. In addition, the model predicts the existence of the extra neutral CP-even scalar boson and the charged scalar boson with masses of the order of 1 TeV.

  10. New State of Matter: Heavy Fermion Systems, Quantum Spin Liquids, Quasicrystals, Cold Gases, and High-Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Shaginyan, V. R.; Stephanovich, V. A.; Msezane, A. Z.; Schuck, P.; Clark, J. W.; Amusia, M. Ya.; Japaridze, G. S.; Popov, K. G.; Kirichenko, E. V.

    2017-08-01

    We report on a new state of matter manifested by strongly correlated Fermi systems including various heavy fermion (HF) metals, two-dimensional quantum liquids such as ^3 He films, certain quasicrystals, and systems behaving as quantum spin liquids. Generically, these systems can be viewed as HF systems or HF compounds, in that they exhibit typical behavior of HF metals. At zero temperature, such systems can experience a so-called fermion condensation quantum phase transition (FCQPT). Combining analytical considerations with arguments based entirely on experimental grounds, we argue and demonstrate that the class of HF systems is characterized by universal scaling behavior of their thermodynamic, transport, and relaxation properties. That is, the quantum physics of different HF compounds is found to be universal, emerging irrespective of the individual details of their symmetries, interactions, and microscopic structure. This observed universal behavior reveals the existence of a new state of matter manifest in HF compounds. We propose a simple, realistic model to study the appearance of flat bands in two-dimensional ensembles of ultracold fermionic atoms, interacting with coherent resonant light. It is shown that signatures of these flat bands may be found in peculiarities in their thermodynamic and spectroscopic properties. We also show that the FCQPT, in generating flat bands and altering Fermi surface topology, is an essential progenitor of the exotic behavior of the overdoped high-temperature superconductors represented by La_{2-x}SrxxCuO_4 , whose superconductivity differs from that predicted by the classical Bardeen-Cooper-Schrieffer theory. The theoretical results presented are in good agreement with recent experimental observations, closing the colossal gap between these empirical findings and Bardeen-Cooper-Schrieffer-like theories.

  11. High-magnetic-fields thermodynamics of the heavy-fermion metal YbRh2Si2

    NASA Astrophysics Data System (ADS)

    Shaginyan, V. R.; Popov, K. G.; Stephanovich, V. A.; Fomichev, V. I.; Kirichenko, E. V.

    2011-01-01

    We perform a comprehensive theoretical analysis of the high-magnetic-field behavior of the heavy-fermion (HF) compound YbRh2Si2. At low magnetic fields B, YbRh2Si2 has a quantum critical point related to the suppression of antiferromagnetic ordering at a critical magnetic field B⊥c of B=Bc0sime0.06 T. Our calculations of the thermodynamic properties of YbRh2Si2 in wide magnetic field range from Bc0sime0.06 T to Bsime18 T allow us to straddle a possible metamagnetic transition region and probe the properties of both low-field HF liquid and high-field fully polarized one. Namely, high magnetic fields B~B*~10 T fully polarize the corresponding quasiparticle band generating a Landau-Fermi-liquid (LFL) state and suppressing the HF (actually NFL) one, while at increasing temperatures both the HF state and the corresponding NFL properties are restored. Our calculations are in good agreement with experimental facts and show that the fermion condensation quantum phase transition is indeed responsible for the observed NFL behavior and quasiparticles survive both high temperatures and high magnetic fields.

  12. Full-Gap Superconductivity Robust against Disorder in Heavy-Fermion CeCu_{2}Si_{2}.

    PubMed

    Takenaka, T; Mizukami, Y; Wilcox, J A; Konczykowski, M; Seiro, S; Geibel, C; Tokiwa, Y; Kasahara, Y; Putzke, C; Matsuda, Y; Carrington, A; Shibauchi, T

    2017-08-18

    A key aspect of unconventional pairing by the antiferromagnetic spin-fluctuation mechanism is that the superconducting energy gap must have the opposite sign on different parts of the Fermi surface. Recent observations of non-nodal gap structure in the heavy-fermion superconductor CeCu_{2}Si_{2} were then very surprising, given that this material has long been considered a prototypical example of a superconductor where the Cooper pairing is magnetically mediated. Here we present a study of the effect of controlled point defects, introduced by electron irradiation, on the temperature-dependent magnetic penetration depth λ(T) in CeCu_{2}Si_{2}. We find that the fully gapped state is robust against disorder, demonstrating that low-energy bound states, expected for sign-changing gap structures, are not induced by nonmagnetic impurities. This provides bulk evidence for s_{++}-wave superconductivity without sign reversal.

  13. Full-Gap Superconductivity Robust against Disorder in Heavy-Fermion CeCu2Si2

    NASA Astrophysics Data System (ADS)

    Takenaka, T.; Mizukami, Y.; Wilcox, J. A.; Konczykowski, M.; Seiro, S.; Geibel, C.; Tokiwa, Y.; Kasahara, Y.; Putzke, C.; Matsuda, Y.; Carrington, A.; Shibauchi, T.

    2017-08-01

    A key aspect of unconventional pairing by the antiferromagnetic spin-fluctuation mechanism is that the superconducting energy gap must have the opposite sign on different parts of the Fermi surface. Recent observations of non-nodal gap structure in the heavy-fermion superconductor CeCu2Si2 were then very surprising, given that this material has long been considered a prototypical example of a superconductor where the Cooper pairing is magnetically mediated. Here we present a study of the effect of controlled point defects, introduced by electron irradiation, on the temperature-dependent magnetic penetration depth λ (T ) in CeCu2Si2 . We find that the fully gapped state is robust against disorder, demonstrating that low-energy bound states, expected for sign-changing gap structures, are not induced by nonmagnetic impurities. This provides bulk evidence for s++-wave superconductivity without sign reversal.

  14. Magnetic field dependence of the residual resistivity of the heavy-fermion metal CeCoIn5

    NASA Astrophysics Data System (ADS)

    Shaginyan, V. R.; Msezane, A. Z.; Popov, K. G.; Clark, J. W.; Zverev, M. V.; Khodel, V. A.

    2012-08-01

    An explanation of the paradoxical behavior of the residual resistivity ρ0 of the heavy-fermion metal CeCoIn5 in magnetic fields and under pressure is developed. The source of this behavior is identified as a flattening of the single-particle spectrum, which exerts profound effects on the specific heat, thermal-expansion coefficient, and magnetic susceptibility in the normal state, the specific-heat jump at the point of superconducting phase transition, and other properties of strongly correlated electron systems in solids. It is shown that application of a magnetic field or pressure to a system possessing a flat band leads to a strong suppression of ρ0. Analysis of its measured thermodynamic and transport properties yields direct evidence for the presence of a flat band in CeCoIn5.

  15. Microscopic properties of the heavy-fermion superconductor PuCoIn5 explored by nuclear quadrupole resonance

    NASA Astrophysics Data System (ADS)

    Koutroulakis, G.; Yasuoka, H.; Chudo, H.; Tobash, P. H.; Mitchell, J. N.; Bauer, E. D.; Thompson, J. D.

    2014-05-01

    We report 115In nuclear quadrupolar resonance (NQR) measurements on the heavy-fermion superconductor PuCoIn5, in the temperature range 0.29K ≤ T ≤ 75K. The NQR parameters for the two crystallographically inequivalent In sites are determined, and their temperature dependence is investigated. A linear shift of the quadrupolar frequency with lowering temperature below the critical value Tc is revealed, in agreement with the prediction for composite pairing. The nuclear spin-lattice relaxation rate T1-1(T) clearly signals a superconducting (SC) phase transition at Tc ≃ 2.3 K, with strong spin fluctuations, mostly in-plane, dominating the relaxation process in the normal state near to Tc. Analysis of the T1-1 data in the SC state suggests that PuCoIn5 is a strong-coupling d-wave superconductor.

  16. Tuning the electronic hybridization in the heavy fermion cage compound YbFe2Zn20 with Cd doping

    NASA Astrophysics Data System (ADS)

    Cabrera-Baez, M.; Ribeiro, R. A.; Avila, M. A.

    2016-09-01

    The tuning of the electronic properties of heavy fermion compounds by chemical substitution provides excellent opportunities for further understanding the physics of hybridized ions in crystal lattices. Here we present an investigation on the effects of Cd doping in flux-grown single crystals of the complex intermetallic cage compound YbFe2Zn20, which has been described as a heavy fermion with a Sommerfeld coefficient of 535 mJ mol-1 · K-2. The substitution of Cd for Zn disturbs the system by expanding the unit cell and, in this case, the size of the Zn cages that surround the Yb and Fe. With an increasing amount of Cd, the hybridization between the Yb 4f electrons and the conduction electrons is weakened, as shown by a decrease in the Sommerfeld coefficient, which should be accompanied by a valence shift of the Yb3+ due to the negative chemical pressure effect. This scenario is also supported by the low temperature DC magnetic susceptibility, which is gradually suppressed and shows an increment of the Kondo temperature, based on a shift to higher temperatures of the characteristic broad susceptibility peak. Furthermore, the DC resistivity decreases with the isoelectronic substitution of Cd for Zn, contrary to expectations in an increasingly disordered system, and implying that the valence shift is not related to charge carrier doping. The combined results demonstrate the excellent complementarity between positive physical pressure and negative chemical pressure, and point to a rich playground for exploring the physics and chemistry of strongly correlated electron systems in the general family of Zn20 compounds, despite their structural complexity.

  17. Tuning the electronic hybridization in the heavy fermion cage compound YbFe2Zn20 with Cd doping.

    PubMed

    Cabrera-Baez, M; Ribeiro, R A; Avila, M A

    2016-09-21

    The tuning of the electronic properties of heavy fermion compounds by chemical substitution provides excellent opportunities for further understanding the physics of hybridized ions in crystal lattices. Here we present an investigation on the effects of Cd doping in flux-grown single crystals of the complex intermetallic cage compound YbFe2Zn20, which has been described as a heavy fermion with a Sommerfeld coefficient of 535 mJ mol(-1) · K(-2). The substitution of Cd for Zn disturbs the system by expanding the unit cell and, in this case, the size of the Zn cages that surround the Yb and Fe. With an increasing amount of Cd, the hybridization between the Yb 4f electrons and the conduction electrons is weakened, as shown by a decrease in the Sommerfeld coefficient, which should be accompanied by a valence shift of the Yb(3+) due to the negative chemical pressure effect. This scenario is also supported by the low temperature DC magnetic susceptibility, which is gradually suppressed and shows an increment of the Kondo temperature, based on a shift to higher temperatures of the characteristic broad susceptibility peak. Furthermore, the DC resistivity decreases with the isoelectronic substitution of Cd for Zn, contrary to expectations in an increasingly disordered system, and implying that the valence shift is not related to charge carrier doping. The combined results demonstrate the excellent complementarity between positive physical pressure and negative chemical pressure, and point to a rich playground for exploring the physics and chemistry of strongly correlated electron systems in the general family of Zn20 compounds, despite their structural complexity.

  18. Superconductivity in a heavy fermion system: CeCu2Si2

    NASA Astrophysics Data System (ADS)

    Kapoor, Charu; Tewari, S. P.

    2016-09-01

    Electron elementary excitations in certain inter-metallic rare-earth compounds are heavy electrons with physical characteristics completely different from that of metallic electrons. Using this knowledge, superconductivity has been studied exploiting heavy electron-phonon interaction brought about by Kondo volume collapse. Superconducting transition temperature, Tc, has been computed, in particular, for CeCu2Si2 under different values of observed Kondo temperature and Gruneisen parameter. It is found that one can explain the experimental Tc = 0.6 K, which is consistent with the description of heavy electron elementary excitations.

  19. Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu2Si2

    PubMed Central

    Yamashita, Takuya; Takenaka, Takaaki; Tokiwa, Yoshifumi; Wilcox, Joseph A.; Mizukami, Yuta; Terazawa, Daiki; Kasahara, Yuichi; Kittaka, Shunichiro; Sakakibara, Toshiro; Konczykowski, Marcin; Seiro, Silvia; Jeevan, Hirale S.; Geibel, Christoph; Putzke, Carsten; Onishi, Takafumi; Ikeda, Hiroaki; Carrington, Antony; Shibauchi, Takasada; Matsuda, Yuji

    2017-01-01

    In exotic superconductors, including high-Tc copper oxides, the interactions mediating electron Cooper pairing are widely considered to have a magnetic rather than a conventional electron-phonon origin. Interest in this exotic pairing was initiated by the 1979 discovery of heavy-fermion superconductivity in CeCu2Si2, which exhibits strong antiferromagnetic fluctuations. A hallmark of unconventional pairing by anisotropic repulsive interactions is that the superconducting energy gap changes sign as a function of the electron momentum, often leading to nodes where the gap goes to zero. We report low-temperature specific heat, thermal conductivity, and magnetic penetration depth measurements in CeCu2Si2, demonstrating the absence of gap nodes at any point on the Fermi surface. Moreover, electron irradiation experiments reveal that the superconductivity survives even when the electron mean free path becomes substantially shorter than the superconducting coherence length. This indicates that superconductivity is robust against impurities, implying that there is no sign change in the gap function. These results show that, contrary to long-standing belief, heavy electrons with extremely strong Coulomb repulsions can condense into a fully gapped s-wave superconducting state, which has an on-site attractive pairing interaction. PMID:28691082

  20. Strongly correlated electron physics: From Kondo and spin glasses to heavy fermions, hidden order and quantum phase transitions

    NASA Astrophysics Data System (ADS)

    Bennett, Edmund; Mydosh, J. A.

    2012-09-01

    We summarize the development of strongly correlated electron physics (SCEP) stimu-lated from the 1930's when a strange upturn was found in the electrical resistivity at low temper-atures. It was only in 1965 that this effect was explained as a many-body, spin-flip, scattering of electrons from a magnetic impurity, i.e., the Kondo effect. This marked the beginning of SCEP. When the concentration of these impurities is increased so that they can randomly interact we have the spin glasses and their unconventional, yet classical phase transition. Spin glass physics formed the background know-how for the combination of two ferromagnetic layers separated by a non-magnetic spacer which generated the the giant magnetic resistance and it many applications in com-puter hardware. By fabricating a lattice of the magnetic species, viz., an intermetallic compound based upon certain rare-earth and actinide elements, we then create a heavy Fermi liquid that can support most unusual ground-state behavior, e.g., unconventional superconductivity. This leads to the mysterious and still unexplained "hidden order" phase transition of URu2Si2. Finally, since the heavy fermions commonly exhibit zero temperature phase transitions, aka, quantum phase transitions when tuned with pressure, magnetic field or doping, we are at the summit of today's SCEP - the prime topic of 2012 condensed matter physics.

  1. Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu2Si2.

    PubMed

    Yamashita, Takuya; Takenaka, Takaaki; Tokiwa, Yoshifumi; Wilcox, Joseph A; Mizukami, Yuta; Terazawa, Daiki; Kasahara, Yuichi; Kittaka, Shunichiro; Sakakibara, Toshiro; Konczykowski, Marcin; Seiro, Silvia; Jeevan, Hirale S; Geibel, Christoph; Putzke, Carsten; Onishi, Takafumi; Ikeda, Hiroaki; Carrington, Antony; Shibauchi, Takasada; Matsuda, Yuji

    2017-06-01

    In exotic superconductors, including high-Tc copper oxides, the interactions mediating electron Cooper pairing are widely considered to have a magnetic rather than a conventional electron-phonon origin. Interest in this exotic pairing was initiated by the 1979 discovery of heavy-fermion superconductivity in CeCu2Si2, which exhibits strong antiferromagnetic fluctuations. A hallmark of unconventional pairing by anisotropic repulsive interactions is that the superconducting energy gap changes sign as a function of the electron momentum, often leading to nodes where the gap goes to zero. We report low-temperature specific heat, thermal conductivity, and magnetic penetration depth measurements in CeCu2Si2, demonstrating the absence of gap nodes at any point on the Fermi surface. Moreover, electron irradiation experiments reveal that the superconductivity survives even when the electron mean free path becomes substantially shorter than the superconducting coherence length. This indicates that superconductivity is robust against impurities, implying that there is no sign change in the gap function. These results show that, contrary to long-standing belief, heavy electrons with extremely strong Coulomb repulsions can condense into a fully gapped s-wave superconducting state, which has an on-site attractive pairing interaction.

  2. Comparison of Amberlite IR 120 and dolomite's performances for removal of heavy metals.

    PubMed

    Kocaoba, Sevgi

    2007-08-17

    The presence of heavy metals in the environment is major concern due to their toxicity. Contamination of heavy metals in water supplies has steadily increased over the last years as a result of over population and expansion of industrial activities. A strong cation-exchange resin, Amberlite IR 120 and a natural zeolite, dolomite were used for the removal of lead(II) and cadmium(II). The optimum conditions were determined in a batch system as concentration range was between 5 and 100 mg/L, pH range between 1 and 8, contact time between 5 and 90 min, and the amount of adsorbent was from 0.1 to 1g. A constant stirring speed, 2000 rpm, was chosen during all of the experiments. The optimum conditions were found to be a concentration of 20 mg/L, pH of 5, contact time of 60 min and 0.5 g of adsorbent. Also, for investigation of exchange equilibria different amounts of ion exchange resin and dolomite were contacted with a fixed volume and concentration of a heavy metal bearing solutions. Sorption data have been interpreted in terms of Langmuir and Freundlich equations. The effect of adsorption temperature on the heavy metals adsorption onto dolomite was investigated at three different temperatures (20, 40 and 60 degrees C). Thermodynamic parameters were calculated. The results obtained show that the Amberlite IR 120 strong cation-exchange resin and dolomite performed well for the removal of these heavy metals. As a low cost adsorbent, dolomite can preferable for removal of heavy metals from wastewaters.

  3. LiV2O4: A heavy fermion transition metal oxide

    SciTech Connect

    Kondo, Shinichiro

    1999-02-12

    The format of this dissertation is as follows. In the remainder of Chapter 1, brief introductions and reviews are given to the topics of frustration, heavy fermions and spinels including the precedent work of LiV2O4. In Chapter 2, as a general overview of this work the important publication in Physical Review Letters by the author of this dissertation and collaborators regarding the discovery of the heavy fermion behavior in LiV2O4 is introduced [removed for separate processing]. The preparation methods employed by the author for nine LiV2O4 and two Li1+xTi2-xO4 (x = 0 and 1/3) polycrystalline samples are introduced in Chapter 3. The subsequent structural characterization of the LiV2O4 and Li1+xT2-xO4 samples was done by the author using thermogravimetric analysis (TGA), x-ray diffraction measurements and their structural refinements by the Rietveld analysis. The results of the characterization are detailed in Chapter 3. In Chapter 4 magnetization measurements carried out by the author are detailed. In Chapter 5, after briefly discussing the resistivity measurement results including the single-crystal work by Rogers et al., for the purpose of clear characterization of LiV2O4 it is of great importance to introduce in the following chapters the experiments and subsequent data analyses done by his collaborators. Heat capacity measurements (Chapter 6) were carried out and analyzed by Dr. C.A. Swenson, and modeled theoretically by Dr. D.C. Johnston. In Chapter 7 a thermal expansion study using neutron diffraction by Dr. O. Chmaissem et al. and capacitance dilatometry measurements by Dr. C.A. Swenson are introduced. The data analyses for the thermal expansion study were mainly done by Dr. O. Chmaissem (for neutron diffraction) and Dr. C.A. Swendon (for dilatometry), with assistances by Dr. J

  4. The f-spin physics of rare-earth iron pnictides: influence of d-electron antiferromagnetic order on heavy fermion phase diagram

    SciTech Connect

    Zhu, Jian-xin; Dai, Jianhui; Si, Qimiao

    2009-01-01

    Some of the high {Tc} iron pnictides contain rare-earth elements, raising the question of how the existence and tunability of a d-electron antiferromagnetic order influences the heavy fermion behavior of the f-moments. With CeOFeP and CeOFeAs in mind as prototypes, we derive an extended Anderson lattice model appropriate for these quaternary systems. We show that the Kondo screening of the f-moments are efficiently suppressed by the d-electron ordering. We also argue that, inside the d-electron ordered state (as in CeOFeAs), the f-moments provide a rare realization of a quantum frustrated magnet with competing J{sub 1}-J{sub 2}-J{sub 3} interactions in an effective square lattice. Implications ofr the heavy fermion physics in broader contexts are also discussed.

  5. Study of the electronic structure of Ce-based heavy-fermion systems exposed to the low-energy neutrino dense flux

    NASA Astrophysics Data System (ADS)

    Trapeznikov, V. A.; Shabanova, I. N.; Murin, A. V.

    2008-11-01

    The class of compounds based on f-elements (Ce) attracts great attention because of their unusual properties. They are characterized by a heavy-fermion state, which occurs in them under certain external actions. Heavy-fermion materials have unique properties. The objective of the work is the investigation of a change in the electronic structure in a number of Ce-based systems under the action of a dense neutrino flux in order to develop the technology for the essential change of material properties. To increase the density of the neutrino flux by several orders of magnitude, the phenomenon of diffraction is used. The investigation of the electronic structure of Ce-based systems on the electron magnetic spectrometer using the x-ray electron method and the calculations of the density of states at different temperatures has shown the decrease in the intensity of the localized resonance maximum near Fermi level with increasing temperature.

  6. Ferromagnetic quantum critical point in the heavy-fermion metal YbNi4(P(1-x)As(x))2.

    PubMed

    Steppke, Alexander; Küchler, Robert; Lausberg, Stefan; Lengyel, Edit; Steinke, Lucia; Borth, Robert; Lühmann, Thomas; Krellner, Cornelius; Nicklas, Michael; Geibel, Christoph; Steglich, Frank; Brando, Manuel

    2013-02-22

    Unconventional superconductivity and other previously unknown phases of matter exist in the vicinity of a quantum critical point (QCP): a continuous phase change of matter at absolute zero. Intensive theoretical and experimental investigations on itinerant systems have shown that metallic ferromagnets tend to develop via either a first-order phase transition or through the formation of intermediate superconducting or inhomogeneous magnetic phases. Here, through precision low-temperature measurements, we show that the Grüneisen ratio of the heavy fermion metallic ferromagnet YbNi(4)(P(0.92)As(0.08))(2) diverges upon cooling to T = 0, indicating a ferromagnetic QCP. Our observation that this kind of instability, which is forbidden in d-electron metals, occurs in a heavy fermion system will have a large impact on the studies of quantum critical materials.

  7. Electron-spin-resonance investigation of the heavy-fermion compound Ce(Cu1-xNix)2Ge2

    NASA Astrophysics Data System (ADS)

    Krug von Nidda, H.-A.; Schütz, A.; Heil, M.; Elschner, B.; Loidl, A.

    1998-06-01

    The heavy-fermion compound Ce(Cu1-xNix)2Ge2 is investigated by Gd3+ electron spin resonance (ESR) within the whole concentration range (0<=x<=1). The Kondo-lattice system exhibits an alloying-induced transition from an antiferromagnetically ordered heavy-fermion ground state (x=0) to pure Kondo-like behavior with strongly enhanced effective masses (x=1). The temperature dependence of the ESR linewidth ΔH allows one to distinguish between the different ground states. The nature of the magnetic order changes significantly from concentrations x<~0.5 to x>0.5. The ESR data provide some further experimental evidence for a transition from a local-moment type (x<0.5) to some kind of itinerant heavy-fermion band magnetism (0.5

  8. Hybridization gap and dual nature of the heavy-fermion compound UPd2Al3 via quasiparticle scattering spectroscopy

    DOE PAGES

    Jaggi, N. K.; Mehio, O.; Dwyer, M.; ...

    2017-04-17

    We present results from point-contact spectroscopy of the antiferromagnetic heavy-fermion superconductor UPd2Al3 : Conductance spectra are taken from single crystals with two major surface orientations as a function of temperature and magnetic field and analyzed using a theory of cotunneling into an Anderson lattice. Spectroscopic signatures are clearly identified, including the distinct asymmetric double-peak structure arising from the opening of a hybridization gap when a coherent heavy-Fermi liquid is formed. Both the hybridization gap, found to be 7.2 ± 0.3 meV at 4 K, and the conductance enhancement above a flat background decrease upon increasing temperature. While the hybridization gapmore » is extrapolated to remain finite up to ~28 K, close to the temperature around which the magnetic susceptibility displays a broad peak, the conductance enhancement vanishes at ~18 K, slightly above the antiferromagnetic transition temperature (T N ≈ 14 K) . This rapid decrease of the conductance enhancement is understood as a consequence of the junction drifting away from the ballistic regime due to increased scattering off magnons associated with the localized U 5 f electrons. This shows that while the hybridization gap opening is not directly associated with the antiferromagnetic ordering, its visibility in the conductance is greatly affected by the temperature-dependent magnetic excitations. Our findings are not only consistent with the 5 f dual-nature picture in the literature but also shed new light on the interplay between the itinerant and localized electrons in UPd2Al3 .« less

  9. Hybridization gap in the heavy-fermion compound UP d2A l3 via quasiparticle scattering spectroscopy

    NASA Astrophysics Data System (ADS)

    Jaggi, N. K.; Mehio, O.; Dwyer, M.; Greene, L. H.; Baumbach, R. E.; Tobash, P. H.; Bauer, E. D.; Thompson, J. D.; Park, W. K.

    2017-04-01

    We present results from point-contact spectroscopy of the antiferromagnetic heavy-fermion superconductor UP d2A l3 : Conductance spectra are taken from single crystals with two major surface orientations as a function of temperature and magnetic field and analyzed using a theory of cotunneling into an Anderson lattice. Spectroscopic signatures are clearly identified, including the distinct asymmetric double-peak structure arising from the opening of a hybridization gap when a coherent heavy-Fermi liquid is formed. Both the hybridization gap, found to be 7.2 ±0.3 meV at 4 K, and the conductance enhancement above a flat background decrease upon increasing temperature. While the hybridization gap is extrapolated to remain finite up to ˜28 K, close to the temperature around which the magnetic susceptibility displays a broad peak, the conductance enhancement vanishes at ˜18 K, slightly above the antiferromagnetic transition temperature (TN≈14 K ) . This rapid decrease of the conductance enhancement is understood as a consequence of the junction drifting away from the ballistic regime due to increased scattering off magnons associated with the localized U 5 f electrons. This shows that while the hybridization gap opening is not directly associated with the antiferromagnetic ordering, its visibility in the conductance is greatly affected by the temperature-dependent magnetic excitations. Our findings are not only consistent with the 5 f dual-nature picture in the literature but also shed new light on the interplay between the itinerant and localized electrons in UP d2A l3 .

  10. Divergence of the Grüneisen Parameter and Magnetocaloric Effect at Heavy Fermion Quantum Critical Points

    NASA Astrophysics Data System (ADS)

    Gegenwart, P.; Tokiwa, Y.; Donath, J. G.; Küchler, R.; Bergmann, C.; Jeevan, H. S.; Bauer, E. D.; Sarrao, J. L.; Geibel, C.; Steglich, F.

    2010-10-01

    At any pressure sensitive quantum critical point (QCP) the thermal expansion is more singular than the specific heat leading to a divergence of the Grüneisen parameter. For a magnetic field sensitive QCP, the complementary property is the magnetic Grüneisen ratio which equals the magnetocaloric effect. Here we use both properties to investigate magnetic QCPs in different heavy fermion (HF) metals starting from CeNi2Ge2. The influence of dimensionality on quantum criticality is addressed by the comparison of cubic CeIn3- x Sn x with layered CeMIn5- x Sn x (M = Co, Rh) systems, in which Sn doping both acts as tuning parameter and introduces slight disorder. Near the field-tuned QCP in undoped CeCoIn5 a crossover scale T ⋆ is discovered which separates 2D (at T> T ⋆) from 3D (at T< T ⋆) quantum criticality. Disorder, introduced by Sn-doping, is found to increase T ⋆, stabilizing 3D behavior. We also compare the magnetic Grüneisen ratio in the approach of the field-tuned QCP in YbRh2Si2 with zero-field Grüneisen parameter data on YbRh2(Si1- x Ge x )2 ( x=0, x=0.05). Both properties indicate quantum criticality incompatible with the predictions of the itinerant theory.

  11. Heavy-Fermion Compound of the Ternary Phosphide Ce2Pt8P with a Non-Centrosymmetric Structure

    NASA Astrophysics Data System (ADS)

    Kase, Naoki; Furukawa, Shoh; Nakano, Tomohito; Takeda, Naoya

    2017-01-01

    The low-temperature properties of Ce2Pt8P are studied by magnetic susceptibility χ(T), electrical resistivity ρ(T), and specific heat C(T) measurements. The crystal structure is considered to be analogs of the CePt3Si-type structure. From the magnetic susceptibility χ(T), the effective paramagnetic moment μeff is estimated to be 2.30 μB/Ce, suggesting that the valence state of Ce ions is expected to be close to trivalent (Ce3+). The paramagnetic Curie-Weiss temperature θcw is determined to be 12 K. The electrical resistivity ρ(T) shows -ln T dependence with a small slope from 10 to 3 K, which indicates a weak Kondo anomaly. The specific heat exhibits a λ-type anomaly at around T* = 1.0 K, while the magnetic entropy at T* is reduced to 80% of R ln 2. The linear coefficient of specific heat is determined to be 145 mJ/(mol-Ce·K2). From several measurements, Ce2Pt8P can be classified as a moderate heavy-fermion compound. The ground state is far from the quantum-critical point (QCP) compared with CePt3Si. La2Pt8P shows normal metallic behavior and no superconductivity is observed above 0.28 K.

  12. NMR studies on heavy fermion and conventional metal superlattices CeCoIn5/YbCoIn5

    NASA Astrophysics Data System (ADS)

    Yamanaka, T.; Shimozawa, M.; Endo, R.; Mizukami, Y.; Shishido, H.; Terashima, T.; Shibauchi, T.; Matsuda, Y.; Ishida, K.

    2017-04-01

    We performed nuclear magnetic resonance (NMR) experiments on heavy fermion and conventional metal superlattices CeCoIn5/YbCoIn5. We succeeded in identifying the signals arising from CeCoIn5 and YbCoIn5 block layers (BLs) by comparing the spectra of the CeCoIn5/YbCoIn5 superlattices, CeCoIn5 thin film, and YbCoIn5 thin film. Furthermore, we found that the signals of Ce-BLs could be divided into signals arising from interfacial layers and inner layers even in one Ce-BL by comparing the spectra of two CeCoIn5/YbCoIn5 superlattices with different thickness of the Ce-BLs. A comparison of the spectra of the superlattices with different Ce-BL thickness and field dependence of nuclear-spin lattice relaxation rate 1/T1 indicate that antiferromagnetic spin fluctuations at the interfacial site are more suppressed than those at the inner layer site even in the Ce-BLs.

  13. Nodal quasiparticle dynamics in the heavy fermion superconductor CeCoIn₅ revealed by precision microwave spectroscopy.

    PubMed

    Truncik, C J S; Huttema, W A; Turner, P J; Ozcan, S; Murphy, N C; Carrière, P R; Thewalt, E; Morse, K J; Koenig, A J; Sarrao, J L; Broun, D M

    2013-01-01

    CeCoIn₅ is a heavy fermion superconductor with strong similarities to the high-Tc cuprates, including quasi-two-dimensionality, proximity to antiferromagnetism and probable d-wave pairing arising from a non-Fermi-liquid normal state. Experiments allowing detailed comparisons of their electronic properties are of particular interest, but in most cases are difficult to realize, due to their very different transition temperatures. Here we use low-temperature microwave spectroscopy to study the charge dynamics of the CeCoIn₅ superconducting state. The similarities to cuprates, in particular to ultra-clean YBa₂Cu₃O(y), are striking: the frequency and temperature dependence of the quasiparticle conductivity are instantly recognizable, a consequence of rapid suppression of quasiparticle scattering below T(c); and penetration-depth data, when properly treated, reveal a clean, linear temperature dependence of the quasiparticle contribution to superfluid density. The measurements also expose key differences, including prominent multiband effects and a temperature-dependent renormalization of the quasiparticle mass.

  14. Crossover from a heavy fermion to intermediate valence state in noncentrosymmetric Yb2Ni12(P,As)7

    NASA Astrophysics Data System (ADS)

    Jiang, W. B.; Yang, L.; Guo, C. Y.; Hu, Z.; Lee, J. M.; Smidman, M.; Wang, Y. F.; Shang, T.; Cheng, Z. W.; Gao, F.; Ishii, H.; Tsuei, K. D.; Liao, Y. F.; Lu, X.; Tjeng, L. H.; Chen, J. M.; Yuan, H. Q.

    2015-12-01

    We report measurements of the physical properties and electronic structure of the hexagonal compounds Yb2Ni12Pn7 (Pn = P, As) by measuring the electrical resistivity, magnetization, specific heat and partial fluorescence yield x-ray absorption spectroscopy (PFY-XAS). These demonstrate a crossover upon reducing the unit cell volume, from an intermediate valence state in Yb2Ni12As7 to a heavy-fermion paramagnetic state in Yb2Ni12P7, where the Yb is nearly trivalent. Application of pressure to Yb2Ni12P7 suppresses TFL, the temperature below which Fermi liquid behavior is recovered, suggesting the presence of a quantum critical point (QCP) under pressure. However, while there is little change in the Yb valence of Yb2Ni12P7 up to 30 GPa, there is a strong increase for Yb2Ni12As7 under pressure, before a near constant value is reached. These results indicate that any magnetic QCP in this system is well separated from strong valence fluctuations. The pressure dependence of the valence and lattice parameters of Yb2Ni12As7 are compared and at 1 GPa, there is an anomaly in the unit cell volume as well as a change in the slope of the Yb valence, indicating a correlation between structural and electronic changes.

  15. Ferromagnetic quantum critical point in heavy-fermion iron oxypnictide Ce(Ru(1-x)Fe(x))PO.

    PubMed

    Kitagawa, S; Ishida, K; Nakamura, T; Matoba, M; Kamihara, Y

    2012-11-30

    We have performed (31)P-NMR measurements on Ce(Ru(1-x)Fe(x))PO in order to investigate ferromagnetic (FM) quantum criticality, since a heavy-fermion (HF) ferromagnet CeRuPO with a two-dimensional structure turns into a HF paramagnet by an isovalent Fe substitution for Ru. We found that Ce(Ru(0.15)Fe(0.85))PO shows critical fluctuations down to ~0.3 K, as well as the continuous suppression of Curie temperature and the ordered moments by the Fe substitution. These experimental results suggest the presence of a FM quantum critical point (QCP) at x~0.86, which is a rare example among itinerant ferromagnets. In addition, we point out that the critical behaviors in Ce(Ru(0.15)Fe(0.85))PO share a similarity with those in YbRh(2)Si(2), where the local criticality of f electrons has been discussed. We reveal that Ce(Ru(1-x)Fe(x))PO is a new system to study FM quantum criticality in HF compounds.

  16. Intense low-energy ferromagnetic fluctuations in the antiferromagnetic heavy-fermion metal CeB6.

    PubMed

    Jang, Hoyoung; Friemel, G; Ollivier, J; Dukhnenko, A V; Shitsevalova, N Yu; Filipov, V B; Keimer, B; Inosov, D S

    2014-07-01

    Heavy-fermion metals exhibit a plethora of low-temperature ordering phenomena . Among these are the so-called hidden-order phases that, in contrast to conventional magnetic order, are invisible to standard neutron diffraction experiments. One of the structurally most simple hidden-order compounds, CeB6, has been intensively studied for an elusive phase that was attributed to the antiferroquadrupolar ordering of cerium-4f moments . As the ground state of CeB6 is characterized by a more conventional antiferromagnetic (AFM) order , the low-temperature physics of this system has generally been assumed to be governed solely by AFM interactions between the dipolar and multipolar Ce moments . Here we overturn this established picture by observing an intense ferromagnetic (FM) low-energy collective mode that dominates the magnetic excitation spectrum of CeB6. Inelastic neutron-scattering data reveal that the intensity of this FM excitation significantly exceeds that of conventional spin-wave magnons emanating from the AFM wavevectors, thus placing CeB6 much closer to a FM instability than previously anticipated. This propensity for ferromagnetism may account for much of the unexplained behaviour of CeB6, and should lead to a re-examination of existing theories that have so far largely neglected the role of FM interactions.

  17. Crossover from a heavy fermion to intermediate valence state in noncentrosymmetric Yb2Ni12(P,As)7.

    PubMed

    Jiang, W B; Yang, L; Guo, C Y; Hu, Z; Lee, J M; Smidman, M; Wang, Y F; Shang, T; Cheng, Z W; Gao, F; Ishii, H; Tsuei, K D; Liao, Y F; Lu, X; Tjeng, L H; Chen, J M; Yuan, H Q

    2015-12-02

    We report measurements of the physical properties and electronic structure of the hexagonal compounds Yb2Ni12Pn7 (Pn = P, As) by measuring the electrical resistivity, magnetization, specific heat and partial fluorescence yield x-ray absorption spectroscopy (PFY-XAS). These demonstrate a crossover upon reducing the unit cell volume, from an intermediate valence state in Yb2Ni12As7 to a heavy-fermion paramagnetic state in Yb2Ni12P7, where the Yb is nearly trivalent. Application of pressure to Yb2Ni12P7 suppresses TFL, the temperature below which Fermi liquid behavior is recovered, suggesting the presence of a quantum critical point (QCP) under pressure. However, while there is little change in the Yb valence of Yb2Ni12P7 up to 30 GPa, there is a strong increase for Yb2Ni12As7 under pressure, before a near constant value is reached. These results indicate that any magnetic QCP in this system is well separated from strong valence fluctuations. The pressure dependence of the valence and lattice parameters of Yb2Ni12As7 are compared and at 1 GPa, there is an anomaly in the unit cell volume as well as a change in the slope of the Yb valence, indicating a correlation between structural and electronic changes.

  18. Multipolar phases and magnetically hidden order: review of the heavy-fermion compound Ce1-x La x B6.

    PubMed

    Cameron, Alistair S; Friemel, Gerd; Inosov, Dmytro S

    2016-06-01

    Cerium hexaboride is a cubic f-electron heavy-fermion compound that displays a rich array of low-temperature magnetic ordering phenomena which have been the subject of investigation for more than 50 years. Its complex behaviour is the result of competing interactions, with both itinerant and local electrons playing important roles. Investigating this material has proven to be a substantial challenge, in particular because of the appearance of a 'magnetically hidden order' phase, which remained elusive to neutron-scattering investigations for many years. It was not until the development of modern x-ray scattering techniques that the long suspected multipolar origin of this phase was confirmed. Doping with non-magnetic lanthanum dilutes the magnetic cerium sublattice and reduces the f-electron count, bringing about substantial changes to the ground state with the emergence of new phases and quantum critical phenomena. To this day, Ce1-x La x B6 and its related compounds remain a subject of intense interest. Despite the substantial progress in understanding their behaviour, they continue to reveal new and unexplained physical phenomena. Here we present a review of the accumulated body of knowledge on this family of materials in order to provide a firm standpoint for future investigations.

  19. Optical Spectroscopy of Strongly Correlated (MOTT-HUBBARD, Heavy-Fermion, Unconventional Superconductor) Materials Tuned Pressure

    SciTech Connect

    Goncharov, A; Struzhkin, V V

    2003-11-12

    During the past years, the Co-PI's have been responsible for the development and operation of optical techniques (Raman, IR, fluorescence, absorption and reflectance spectroscopy at ultrahigh pressures and high and low temperatures) which have proven to be extremely powerful for studying low-Z, molecular solids including hydrogen, ice, etc. (see results below). Meanwhile, it has become increasingly clear that optical spectroscopy has an equally extraordinary potential for studying metals and superconductors at ultrahigh pressures, thus the result will have a major impact on material research. However, because of the extreme difference in optical properties of opaque metals and transparent insulating molecular solids, successful accomplishment of the present project will require substantial effort in improving the present equipment and developing new techniques, and funds for this are requested here. Below we provide a short description of the work done and techniques developed during the last years. We also propose to explore new frontiers in compressed materials close to the insulator-metal boundaries, spin-crossover, and other quantum critical points.

  20. Hidden magnetism and quantum criticality in the heavy fermion superconductor CeRhIn5.

    PubMed

    Park, Tuson; Ronning, F; Yuan, H Q; Salamon, M B; Movshovich, R; Sarrao, J L; Thompson, J D

    2006-03-02

    With only a few exceptions that are well understood, conventional superconductivity does not coexist with long-range magnetic order (for example, ref. 1). Unconventional superconductivity, on the other hand, develops near a phase boundary separating magnetically ordered and magnetically disordered phases. A maximum in the superconducting transition temperature T(c) develops where this boundary extrapolates to zero Kelvin, suggesting that fluctuations associated with this magnetic quantum-critical point are essential for unconventional superconductivity. Invariably, though, unconventional superconductivity masks the magnetic phase boundary when T < T(c), preventing proof of a magnetic quantum-critical point. Here we report specific-heat measurements of the pressure-tuned unconventional superconductor CeRhIn5 in which we find a line of quantum-phase transitions induced inside the superconducting state by an applied magnetic field. This quantum-critical line separates a phase of coexisting antiferromagnetism and superconductivity from a purely unconventional superconducting phase, and terminates at a quantum tetracritical point where the magnetic field completely suppresses superconductivity. The T --> 0 K magnetic field-pressure phase diagram of CeRhIn5 is well described with a theoretical model developed to explain field-induced magnetism in the high-T(c) copper oxides, but in which a clear delineation of quantum-phase boundaries has not been possible. These experiments establish a common relationship among hidden magnetism, quantum criticality and unconventional superconductivity in copper oxides and heavy-electron systems such as CeRhIn5.

  1. Li NMR study of heavy-fermion LiV2O4 containing magnetic defects

    SciTech Connect

    Zong, X.; Das, S.; Borsa, F.; Vannette, M.; Prozorov, R.; Schmalian, J.; Johnston, D.

    2008-04-21

    We present a systematic study of the variations of the {sup 7}Li NMR properties versus magnetic defect concentration up to 0.83 mol% within the spinel structure of polycrystalline powder samples and a collection of small single crystals of LiV2O4 in the temperature range from 0.5 to 4.2 K. We also report static magnetization measurements and ac magnetic susceptibility measurements at 14 MHz on the samples at low temperatures. Both the NMR spectrum and nuclear spin-lattice relaxation rate are inhomogeneous in the presence of the magnetic defects. The NMR data for the powders are well explained by assuming that (i) there is a random distribution of magnetic point defects, (ii) the same heavy Fermi liquid is present in the samples containing the magnetic defects as in magnetically pure LiV2O4, and (iii) the influences of the magnetic defects and of the Fermi liquid on the magnetization and NMR properties are separable. In the single crystals, somewhat different behaviors are observed. Remarkably, the magnetic defects in the powder samples show evidence of spin freezing below T {approx} 1.0 K, whereas in the single crystals with similar magnetic defect concentration no spin freezing was found down to 0.5 K. Thus different types of magnetic defects and/or interactions between them appear to arise in the powders versus the crystals, possibly due to the substantially different synthesis conditions of the powders and crystals.

  2. Anderson lattice with explicit Kondo coupling revisited: metamagnetism and the field-induced suppression of the heavy fermion state.

    PubMed

    Howczak, Olga; Spałek, Jozef

    2012-05-23

    We apply the extended (statistically consistent, SCA) Gutzwiller-type approach to the periodic Anderson model (PAM) in an applied magnetic field and in the strong-correlation limit. The finite-U corrections are included systematically by transforming the PAM into the form with the Kondo-type interaction and the residual hybridization, both appearing at the same time and on equal footing. This effective Hamiltonian represents the essence of our Anderson-Kondo lattice model. We show that in ferromagnetic phases the low-energy single-particle states are strongly affected by the presence of the applied magnetic field. We also find that for large values of hybridization strength the system enters the so-called locked heavy fermion state introduced earlier. In this state the chemical potential lies in the majority-spin hybridization gap and, as a consequence, the system evolution is insensitive to further increase of the applied field. However, for a sufficiently strong magnetic field, the system transforms from the locked state to the fully spin-polarized phase. This is accompanied by a metamagnetic transition, as well as by a drastic reduction of the effective mass of the quasiparticles. In particular, we observe no effective mass enhancement in the fully polarized state. The findings are in overall agreement with experimental results for the Ce compounds in high magnetic fields. The mass enhancement for the spin-minority electrons may also diminish with the increasing field, unlike for the quasiparticle states in a single narrow band in the same limit of strong correlations.

  3. High-resolution x-ray diffraction study of the heavy-fermion compound YbBiPt

    SciTech Connect

    Ueland, B. G.; Saunders, S. M.; Bud'ko, S. L.; Schmiedeshoff, G. M.; Canfield, P. C.; Kreyssig, A.; Goldman, A. I.

    2015-11-30

    In this study, YbBiPt is a heavy-fermion compound possessing significant short-range antiferromagnetic correlations below a temperature of T*=0.7K, fragile antiferromagnetic order below TN = 0.4K, a Kondo temperature of TK ≈ 1K, and crystalline-electric-field splitting on the order of E/kB = 1 – 10K. Whereas the compound has a face-centered-cubic lattice at ambient temperature, certain experimental data, particularly those from studies aimed at determining its crystalline-electric-field scheme, suggest that the lattice distorts at lower temperature. Here, we present results from high-resolution, high-energy x-ray diffraction experiments which show that, within our experimental resolution of ≈ 6 – 10 × 10–5 Å, no structural phase transition occurs between T = 1.5 and 50 K. In combination with results from dilatometry measurements, we further show that the compound's thermal expansion has a minimum at ≈ 18 K and a region of negative thermal expansion for 9 ≲ T ≲ 18 K. Despite diffraction patterns taken at 1.6 K which indicate that the lattice is face-centered cubic and that the Yb resides on a crystallographic site with cubic point symmetry, we demonstrate that the linear thermal expansion may be modeled using crystalline-electric-field level schemes appropriate for Yb3+ residing on a site with either cubic or less than cubic point symmetry.

  4. High-resolution x-ray diffraction study of the heavy-fermion compound YbBiPt

    DOE PAGES

    Ueland, B. G.; Saunders, S. M.; Bud'ko, S. L.; ...

    2015-11-30

    In this study, YbBiPt is a heavy-fermion compound possessing significant short-range antiferromagnetic correlations below a temperature of T*=0.7K, fragile antiferromagnetic order below TN = 0.4K, a Kondo temperature of TK ≈ 1K, and crystalline-electric-field splitting on the order of E/kB = 1 – 10K. Whereas the compound has a face-centered-cubic lattice at ambient temperature, certain experimental data, particularly those from studies aimed at determining its crystalline-electric-field scheme, suggest that the lattice distorts at lower temperature. Here, we present results from high-resolution, high-energy x-ray diffraction experiments which show that, within our experimental resolution of ≈ 6 – 10 × 10–5 Å,more » no structural phase transition occurs between T = 1.5 and 50 K. In combination with results from dilatometry measurements, we further show that the compound's thermal expansion has a minimum at ≈ 18 K and a region of negative thermal expansion for 9 ≲ T ≲ 18 K. Despite diffraction patterns taken at 1.6 K which indicate that the lattice is face-centered cubic and that the Yb resides on a crystallographic site with cubic point symmetry, we demonstrate that the linear thermal expansion may be modeled using crystalline-electric-field level schemes appropriate for Yb3+ residing on a site with either cubic or less than cubic point symmetry.« less

  5. Magnetism, f-electron localization and superconductivity in 122-type heavy-fermion metals.

    PubMed

    Steglich, F; Arndt, J; Stockert, O; Friedemann, S; Brando, M; Klingner, C; Krellner, C; Geibel, C; Wirth, S; Kirchner, S; Si, Q

    2012-07-25

    Both CeCu2Si2 and YbRh2Si2 crystallize in the tetragonal ThCr2Si2 crystal structure. Recent neutron-scattering results on normal-state CeCu2Si2 reveal a slowing down of the quasielastic response which complies with the scaling expected for a quantum critical point (QCP) of itinerant, i.e., three-dimensional spin-density-wave (SDW), type. This interpretation is in full agreement with the non-Fermi-liquid behavior observed in transport and thermodynamic measurements. The momentum dependence of the magnetic excitation spectrum reveals two branches of an overdamped dispersive mode whose coupling to the heavy charge carriers is strongly retarded. These overdamped spin fluctuations are considered to be the driving force for superconductivity in CeCu2Si2 (Tc = 600 mK). The weak antiferromagnet YbRh2Si2 (TN = 70 mK) exhibits a magnetic-field-induced QCP at BN = 0.06 T (B⊥c). There is no indication of superconductivity down to T = 10 mK. The magnetic QCP appears to concur with a breakdown of the Kondo effect. Doping-induced variations of the average unit-cell volume result in a detachment of the magnetic and electronic instabilities. A comparison of the properties of these isostructural compounds suggests that 3D SDW QCPs are favorable for unconventional superconductivity. The question whether a Kondo-breakdown QCP may also give rise to superconductivity, however, remains to be clarified.

  6. Mid-IR absorption sensing of heavy water using a silicon-on-sapphire waveguide.

    PubMed

    Singh, Neetesh; Casas-Bedoya, Alvaro; Hudson, Darren D; Read, Andrew; Mägi, Eric; Eggleton, Benjamin J

    2016-12-15

    We demonstrate a compact silicon-on-sapphire (SOS) strip waveguide sensor for mid-IR absorption spectroscopy. This device can be used for gas and liquid sensing, especially to detect chemically similar molecules and precisely characterize extremely absorptive liquids that are difficult to detect by conventional infrared transmission techniques. We reliably measure concentrations up to 0.25% of heavy water (D2O) in a D2O-H2O mixture at its maximum absorption band at around 4 μm. This complementary metal-oxide-semiconductor (CMOS) compatible SOS D2O sensor is promising for applications such as measuring body fat content or detection of coolant leakage in nuclear reactors.

  7. A comparison of the structure and localized magnetism in Ce{sub 2}PdGa{sub 12} with the heavy fermion CePdGa{sub 6}

    SciTech Connect

    Macaluso, Robin T.; Millican, Jasmine N.; Nakatsuji, Satoru; Lee, Han-Oh; Carter, B.; Moreno, Nelson O.; Fisk, Zachary; Chan, Julia Y. . E-mail: jchan@lsu.edu

    2005-11-15

    Single crystals of Ce{sub 2}PdGa{sub 12} have been synthesized in Ga flux and characterized by X-ray diffraction. This compound crystallizes in the tetragonal P4/nbm space group, Z=2 with lattice parameters of a=6.1040(2)A and c=15.5490(6)A. It shows strongly anisotropic magnetism and orders antiferromagnetically at T{sub N}{approx}11K. A field-induced metamagnetic transition to the ferromagnetic state is observed below T{sub N}. Structure-property relationships with the related heavy-fermion antiferromagnet CePdGa{sub 6} are discussed.

  8. Angular position of nodes in the superconducting gap of quasi-2D heavy-fermion superconductor CeCoIn5.

    PubMed

    Izawa, K; Yamaguchi, H; Matsuda, Y; Shishido, H; Settai, R; Onuki, Y

    2001-07-30

    The thermal conductivity of the heavy-fermion superconductor CeCoIn5 has been studied in a magnetic field rotating within the 2D planes. A clear fourfold symmetry of the thermal conductivity which is characteristic of a superconducting gap with nodes along the ( +/- pi,+/- pi) directions is resolved. The thermal conductivity measurement also reveals a first-order transition at H(c2), indicating a Pauli limited superconducting state. These results indicate that the symmetry most likely belongs to d(x(2)-y(2)), implying that the anisotropic antiferromagnetic fluctuation is relevant to the superconductivity.

  9. Connection between charge fluctuations and the coherent temperature in the heavy-fermion system SmOs4Sb12: a {121, 123}Sb NQR study.

    PubMed

    Kotegawa, H; Hidaka, H; Kobayashi, T C; Kikuchi, D; Sugawara, H; Sato, H

    2007-10-12

    We report {121, 123}Sb nuclear quadrupole resonance measurements under pressure in a novel heavy fermion (HF) system SmOs4Sb12. The nuclear spin-spin relaxation rate 1/T{2} exhibits a distinct peak near the coherent temperature of the Kondo effect. The isotope effect of 121Sb and 123Sb indicates that the peak in 1/T{2} is electrical in origin. The connection between the peak in 1/T{2} and the development of coherency of the Kondo effect is robust even under pressure. It is conjectured that charge fluctuation plays an important role in forming the HF state in SmOs4Sb12.

  10. Neutron diffraction study of magnetic field induced behavior in the heavy Fermion Ce3Co4Sn13

    SciTech Connect

    Christianson, Andrew D; Goremychkin, E. A.; Gardner, J. S.; Kang, H. J.; Chung, J.-H.; Manuel, P.; Thompson, J. D.; Sarrao, J. L.; Lawrence, J. M.

    2008-01-01

    The specific heat of Ce3Co4Sn13 exhibits a crossover from heavy Fermion behavior with antiferromagnetic correlations at low field to single impurity Kondo behavior above 2 T. We have performed neutron diffraction measurements in magnetic fields up to 6 Tesla on single crystal samples. The (001) position shows a dramatic increase in intensity in field which appears to arise from static polarization of the 4f level and which at 0.14 K also exhibits an anomaly near 2T reflecting the crossover to single impurity behavior.

  11. Extended nuclear quadrupole resonance study of the heavy-fermion superconductor PuCoGa5

    SciTech Connect

    Koutroulakis, Georgios; Yasuoka, Hiroshi; Tobash, Paul H.; Mitchell, Jeremy Neil; Bauer, Eric Dietzgen; Thompson, Joe David

    2016-10-10

    PuCoGa5 has emerged as a prototypical heavy-fermion superconductor, with its transition temperature (Tc ≃ 18.5 K) being the highest amongst such materials. Nonetheless, a clear description as to what drives the superconducting pairing is still lacking, rendered complicated by the notoriously intricate nature of plutonium's 5f valence electrons. Here, we present a detailed 69,71Ga nuclear quadrupole resonance (NQR) study of PuCoGa5, concentrating on the system's normal state properties near to Tc and aiming to detect distinct signatures of possible pairing mechanisms. In particular, the quadrupole frequency and spin-lattice relaxation rate were measured for the two crystallographically inequivalent Ga sites and for both Ga isotopes, in the temperature range 1.6–300 K. No evidence of significant charge fluctuations is found from the NQR observables. On the contrary, the low-energy dynamics is dominated by anisotropic spin fluctuations with strong, nearly critical, in-plane character, which are effectively identical to the case of the sister compound PuCoIn5. Lastly, these findings are discussed within the context of different theoretical proposals for the unconventional pairing mechanism in heavy-fermion superconductors.

  12. Robust upward dispersion of the neutron spin resonance in the heavy fermion superconductor Ce1-xYbxCoIn5

    NASA Astrophysics Data System (ADS)

    Song, Yu; van Dyke, John; Lum, I. K.; White, B. D.; Jang, Sooyoung; Yazici, Duygu; Shu, L.; Schneidewind, A.; Čermák, Petr; Qiu, Y.; Maple, M. B.; Morr, Dirk K.; Dai, Pengcheng

    2016-09-01

    The neutron spin resonance is a collective magnetic excitation that appears in the unconventional copper oxide, iron pnictide and heavy fermion superconductors. Although the resonance is commonly associated with a spin-exciton due to the d(s+/-)-wave symmetry of the superconducting order parameter, it has also been proposed to be a magnon-like excitation appearing in the superconducting state. Here we use inelastic neutron scattering to demonstrate that the resonance in the heavy fermion superconductor Ce1-xYbxCoIn5 with x=0, 0.05 and 0.3 has a ring-like upward dispersion that is robust against Yb-doping. By comparing our experimental data with a random phase approximation calculation using the electronic structure and the momentum dependence of the -wave superconducting gap determined from scanning tunnelling microscopy (STM) for CeCoIn5, we conclude that the robust upward-dispersing resonance mode in Ce1-xYbxCoIn5 is inconsistent with the downward dispersion predicted within the spin-exciton scenario.

  13. Magnetic and superconducting properties of a heavy-fermion CeCoIn5 epitaxial film probed by nuclear quadrupole resonance

    NASA Astrophysics Data System (ADS)

    Yamanaka, Takayoshi; Shimozawa, Masaaki; Shishido, Hiroaki; Kitagawa, Shunsaku; Ikeda, Hiroaki; Shibauchi, Takasada; Terashima, Takahito; Matsuda, Yuji; Ishida, Kenji

    2017-08-01

    Since the progress in the fabrication techniques of thin films of exotic materials such as strongly correlated heavy-fermion compounds, microscopic studies of the magnetic and electronic properties inside the films have been needed. Herein, we report the observation of 115In nuclear quadrupole resonance (NQR) in an epitaxial film of the heavy-fermion superconductor CeCoIn5, for which the microscopic field gradient within the unit cell as well as magnetic and superconducting properties at zero field are evaluated. We find that the nuclear spin-lattice relaxation rate in the film is in excellent agreement with that of bulk crystals, whereas the NQR spectra show noticeable shifts and significant broadening indicating a change in the electric-field distribution inside the film. The analysis implies a displacement of In layers in the film, which, however, does not affect the magnetic fluctuations and superconducting pairing. This implies that inhomogeneity of the electronic field gradient in the film sample causes no pair-breaking effect.

  14. Pressure-induced magnetic transition exceeding 30 K in the Yb-based heavy-fermion β -YbAlB4

    NASA Astrophysics Data System (ADS)

    Tomita, Takahiro; Kuga, Kentaro; Uwatoko, Yoshiya; Nakatsuji, Satoru

    2016-12-01

    Measurements of the electric resistivity ρ (T ) under pressure up to 8 GPa were performed on high-quality single crystals of the Yb-based heavy-fermion system β -YbAlB4 in the temperature range 2 heavy-fermion compounds. The power-law exponent α in ρ =ρ0+A Tα below TM gradually changes from 3/2 to 5/2 with increasing pressure from 2 to 8 GPa. In contrast, the resistivity exhibits a T -linear behavior in the temperature range 2 ≤T ≤20 K and is insensitive to pressure below Pc. In this pressure regime, the magnetization is also nearly independent of pressure and shows no anomaly above 2 K. Our results indicate that a quantum critical point for β -YbAlB4 is also located near Pc in addition to the strange metal region near the ambient pressure.

  15. Electronic properties of a heavy-fermion U (Ru0.92Rh0.08 )2Si2 single crystal

    NASA Astrophysics Data System (ADS)

    Prokeš, K.; Huang, Y.-K.; Reehuis, M.; Klemke, B.; Hoffmann, J.-U.; Sokolowski, A.; de Visser, A.; Mydosh, J. A.

    2017-01-01

    We report the crystal structure and highly anisotropic magnetic, transport, and thermal properties of an exceptionally good single crystal of U (Ru0.92Rh0.08)2Si2 , prepared using a modified Czochralski method. Our study, that also includes neutron diffraction results, shows all the heavy-fermion signatures of pristine URu2Si2 ; however, the superconductivity, hidden order, and remnant weak antiferromagnetic orders are absent. Instead, the ground state of the doped system can be classified as a spin liquid that preserves the heavy-fermion character. U (Ru0.92Rh0.08)2Si2 exhibits a short-range magnetic order distinguished by reflections of a Lorentzian profile at qIII=(1/2 1/2 1/2 ) positions that disappear above ˜15 K. The short-range order seems to be a precursor of a long-range magnetic order that occurs with higher Rh concentration. We indicate that these short-range fluctuations involve, at least partially, inelastic scattering processes.

  16. Heavy fermions, metal-to-insulator transition, and quantum criticality in La y Cu3Ru x Ti4- x O12

    NASA Astrophysics Data System (ADS)

    Riegg, S.; Widmann, S.; Günther, A.; Meir, B.; Wehrmeister, S.; Sterz, S.; Kraetschmer, W.; Ebbinghaus, S. G.; Reller, A.; Büttgen, N.; Krug von Nidda, H.-A.; Loidl, A.

    2015-07-01

    In this work we investigate the solid-solution series La y Cu3Ru x Ti4- x O12. The titanate La2/3Cu3Ti4O12 ( x = 0) is an antiferromagnetic insulator exhibiting colossal dielectric constants, while the ruthenate LaCu3Ru4O12 ( x = 4) is known as a rare d-electron derived heavy-fermion compound. Detailed structural investigations, AC- and DC-magnetization measurements, resistivity, specific-heat, and magnetic-resonance investigations have been performed for all polycrystalline compounds prepared by solid-state synthesis. These experiments have been accompanied by band-structure calculations. Close to the Ru concentration x = 2 we identify a quantum-critical point coinciding with a metal-to-insulator transition. The quantum-critical point separates an insulating spin glass from a paramagnetic metal. Interestingly, there is no evidence for a divergence of the effective mass upon reaching the quantum-critical point from the metallic side. In the paramagnetic metal, Ru behaves like a canonical Kondo ion. While the Ru oxidation state remains stable at + 4 for the whole concentration regime, the Cu valence seems to decrease from + 2 in the insulating antiferromagnet with localized copper spins to a significantly lower value in the metallic heavy-fermion compounds.

  17. Robust upward dispersion of the neutron spin resonance in the heavy fermion superconductor Ce1−xYbxCoIn5

    PubMed Central

    Song, Yu; Van Dyke, John; Lum, I. K.; White, B. D.; Jang, Sooyoung; Yazici, Duygu; Shu, L.; Schneidewind, A.; Čermák, Petr; Qiu, Y.; Maple, M. B.; Morr, Dirk K.; Dai, Pengcheng

    2016-01-01

    The neutron spin resonance is a collective magnetic excitation that appears in the unconventional copper oxide, iron pnictide and heavy fermion superconductors. Although the resonance is commonly associated with a spin-exciton due to the d(s±)-wave symmetry of the superconducting order parameter, it has also been proposed to be a magnon-like excitation appearing in the superconducting state. Here we use inelastic neutron scattering to demonstrate that the resonance in the heavy fermion superconductor Ce1−xYbxCoIn5 with x=0, 0.05 and 0.3 has a ring-like upward dispersion that is robust against Yb-doping. By comparing our experimental data with a random phase approximation calculation using the electronic structure and the momentum dependence of the -wave superconducting gap determined from scanning tunnelling microscopy (STM) for CeCoIn5, we conclude that the robust upward-dispersing resonance mode in Ce1−xYbxCoIn5 is inconsistent with the downward dispersion predicted within the spin-exciton scenario. PMID:27677397

  18. Robust upward dispersion of the neutron spin resonance in the heavy fermion superconductor Ce1–xYbxCoIn5

    DOE PAGES

    Song, Yu; Van Dyke, John; Lum, I. K.; ...

    2016-09-28

    Here, the neutron spin resonance is a collective magnetic excitation that appears in copper oxide, iron pnictide, and heavy fermion unconventional superconductors. Although the resonance is commonly associated with a spin-exciton due to the d(s±)-wave symmetry of the superconducting order parameter, it has also been proposed to be a magnon-like excitation appearing in the superconducting state. Here we use inelastic neutron scattering to demonstrate that the resonance in the heavy fermion superconductor Ce1–xYbxCoIn5 with x=0,0.05,0.3 has a ring-like upward dispersion that is robust against Yb-doping. By comparing our experimental data with random phase approximation calculation using the electronic structure andmore » the momentum dependence of the dx2–y2-wave superconducting gap determined from scanning tunneling microscopy for CeCoIn5, we conclude the robust upward dispersing resonance mode in Ce1–xYbxCoIn5 is inconsistent with the downward dispersion predicted within the spin-exciton scenari« less

  19. Magnetic order and heavy fermion behavior in CePd{sub 1+x}Al{sub 6-x}: Synthesis, structure, and physical properties

    SciTech Connect

    Tobash, Paul H.; Ronning, Filip; Thompson, J.D.; Bobev, Svilen; Bauer, Eric D.

    2010-03-15

    The physical properties including magnetic susceptibility, specific heat, and electrical resistivity of single crystals are reported for the compound CePd{sub 1+x}Al{sub 6-x} (x=0.5) which crystallizes in the tetragonal SrAu{sub 2}Ga{sub 5}-type structure (space group P4/mmm). The compound was grown from an excess of molten Al flux from the respective elements and the crystal structure was established from single-crystal X-ray diffraction. Anomalies in the low temperature specific heat C{sub p}(T) and electrical resistivity rho(T) show that the compound undergoes ferromagnetic order at T{sub C}=2.8 K. In the ordered state, CePd{sub 1.5}Al{sub 5.5} displays heavy fermion behavior with a Sommerfeld coefficient of ca. 500 mJ/mol-K{sup 2}. - Graphical abstract: The compound CePd{sub 1+x}Al{sub 6-x} (x=0.5) has been synthesized and structurally characterized by single-crystal X-ray diffraction. The measured physical properties of temperature and field dependent magnetic susceptibility, specific heat, and electrical resistivity suggests that the compound undergoes ferromagnetic order at ca. 2.8 K and further exhibits relatively heavy fermion behavior with a Sommerfeld coefficient of 500 mJ/mol-K2.

  20. Extended nuclear quadrupole resonance study of the heavy-fermion superconductor PuCoGa5

    SciTech Connect

    Koutroulakis, Georgios; Yasuoka, Hiroshi; Tobash, Paul H.; Mitchell, Jeremy Neil; Bauer, Eric Dietzgen; Thompson, Joe David

    2016-10-10

    PuCoGa5 has emerged as a prototypical heavy-fermion superconductor, with its transition temperature (Tc ≃ 18.5 K) being the highest amongst such materials. Nonetheless, a clear description as to what drives the superconducting pairing is still lacking, rendered complicated by the notoriously intricate nature of plutonium's 5f valence electrons. Here, we present a detailed 69,71Ga nuclear quadrupole resonance (NQR) study of PuCoGa5, concentrating on the system's normal state properties near to Tc and aiming to detect distinct signatures of possible pairing mechanisms. In particular, the quadrupole frequency and spin-lattice relaxation rate were measured for the two crystallographically inequivalent Ga sites and for both Ga isotopes, in the temperature range 1.6–300 K. No evidence of significant charge fluctuations is found from the NQR observables. On the contrary, the low-energy dynamics is dominated by anisotropic spin fluctuations with strong, nearly critical, in-plane character, which are effectively identical to the case of the sister compound PuCoIn5. Lastly, these findings are discussed within the context of different theoretical proposals for the unconventional pairing mechanism in heavy-fermion superconductors.

  1. Robust upward dispersion of the neutron spin resonance in the heavy fermion superconductor Ce1-xYbxCoIn5.

    PubMed

    Song, Yu; Van Dyke, John; Lum, I K; White, B D; Jang, Sooyoung; Yazici, Duygu; Shu, L; Schneidewind, A; Čermák, Petr; Qiu, Y; Maple, M B; Morr, Dirk K; Dai, Pengcheng

    2016-09-28

    The neutron spin resonance is a collective magnetic excitation that appears in the unconventional copper oxide, iron pnictide and heavy fermion superconductors. Although the resonance is commonly associated with a spin-exciton due to the d(s(±))-wave symmetry of the superconducting order parameter, it has also been proposed to be a magnon-like excitation appearing in the superconducting state. Here we use inelastic neutron scattering to demonstrate that the resonance in the heavy fermion superconductor Ce1-xYbxCoIn5 with x=0, 0.05 and 0.3 has a ring-like upward dispersion that is robust against Yb-doping. By comparing our experimental data with a random phase approximation calculation using the electronic structure and the momentum dependence of the -wave superconducting gap determined from scanning tunnelling microscopy (STM) for CeCoIn5, we conclude that the robust upward-dispersing resonance mode in Ce1-xYbxCoIn5 is inconsistent with the downward dispersion predicted within the spin-exciton scenario.

  2. FT-IR Spectra of Antifreeze Glycoproteins in Heavy Water and D2O Ice.

    NASA Astrophysics Data System (ADS)

    Tsvetkova, N. M.; Crowe, J. H.; Feeney, R. H.; Fink, W. H.; Yeh, Yin

    2000-03-01

    This work presents FT-IR studies on the antifreeze glycoprotein (AFGP)/heavy water (D2O) mixtures during freezing and melting. AFGP in the blood serum of polar fish are known to prevent ice crystal growth by a non-colligative mechanism. There are 8 known fractions of AFGP (1 8) that range in molecular mass from 33.7 to 2.6 kD respectively, each composed of alanine-alanine-threonine repeats, with a disaccharide attached to the threonine residue. The smallest peptide (AFGP-8) is structurally different from fractions 1-5 in that it contains proline substituting for alanine in certain positions. Substantial linewidth change of the D20 bending mode (ca. 1210 cm-1) was measured with solutions containing fractions 2-5 during both freezing and thawing cycles, suggesting significant coupling between protein and water molecules. At the same time, the Amide I band between 1620 and 1675 cm-1 shows that 310 helix and random coils are the main conformations of fractions 2-5 and fraction 8 in the presence of ice. In liquid state, b-sheet dominates the secondary structure of AFGP 8, whereas b-sheet and random coil are the main conformations of AFGP 2-5. These results are discussed in terms of the ability of AFGP 2-5 to affect the surface states of ice.

  3. Characterization of the heavy metal pyrochlore lattice superconductor CaIr2.

    PubMed

    Haldolaarachchige, Neel; Gibson, Quinn; Schoop, Leslie M; Luo, Huixia; Cava, R J

    2015-05-13

    We report the electronic properties of the cubic laves phase superconductor CaIr2(Tc = 5.8 K), in which the Ir atoms have a pyrochlore lattice. The estimated superconducting parameters obtained from magnetization and specific heat measurements indicate that CaIr2 is a weakly coupled BCS superconductor. Electronic band structure calculations show that the Ir d-states are dominant at the Fermi level, creating a complex Fermi surface that is impacted substantially by spin-orbit coupling.

  4. Topological basis for understanding the behavior of the heavy-fermion metal β -YbAlB4 under application of magnetic field and pressure

    NASA Astrophysics Data System (ADS)

    Shaginyan, V. R.; Msezane, A. Z.; Popov, K. G.; Clark, J. W.; Khodel, V. A.; Zverev, M. V.

    2016-05-01

    Informative recent measurements on the heavy-fermion metal β -YbAlB4 performed with applied magnetic field and pressure as control parameters are analyzed with the goal of establishing a sound theoretical explanation for the inferred scaling laws and non-Fermi-liquid (NFL) behavior, which demonstrate some unexpected features. Most notably, the robustness of the NFL behavior of the thermodynamic properties and of the anomalous T3 /2 temperature dependence of the electrical resistivity under applied pressure P in zero magnetic field is at variance with the fragility of the NFL phase under application of a field B . We show that a consistent topological basis for this combination of observations, as well as the empirical scaling laws, may be found within fermion-condensation theory in the emergence and destruction of a flat band, and explains that the paramagnetic NFL phase takes place without magnetic criticality, not from quantum critical fluctuations. Schematic T -B and T -P phase diagrams are presented to illuminate this scenario.

  5. CeCu sub 4 A ell and CeCu sub 2 Zn sub 2 A ell : Very heavy fermion systems in high magnetic fields

    SciTech Connect

    Andraka, B.; Kim, J.S. . Dept. of Physics); Stewart, G.R. . Dept. of Physics Augsburg Univ. ); Fisk, Z. )

    1990-01-01

    CeCu{sub 4}A{ell} and CeCu{sub 2}Zn{sub 2}A{ell} are heavy fermion systems with extremely enhanced C/T (specific heat divided by temperature) values of 2.3 and 1.8 J/K{sup 2} respectively as T {yields} 0 K. The field dependence of the low temperature specific heat is also extreme; 11 T reduces C of CeCu{sub 4}A{ell} by more than a factor of five, 12.5 T suppresses C of CeCu{sub 2}Zn{sub 2}A{ell} about seven times. Magnetic field caused changes of the specific heat of CeCu{sub 4}A{ell} are consistent with a single ion Kondo model. Magnetic correlations are at least partially responsible for the enhanced low temperature specific heat of CeCu{sub 2}Zn{sub 2}A{ell}.

  6. Evidence for Coexistence of Bulk Superconductivity and Itinerant Antiferromagnetism in the Heavy Fermion System CeCo(In1−xCdx)5

    PubMed Central

    Howald, Ludovic; Stilp, Evelyn; de Réotier, Pierre Dalmas; Yaouanc, Alain; Raymond, Stéphane; Piamonteze, Cinthia; Lapertot, Gérard; Baines, Christopher; Keller, Hugo

    2015-01-01

    In the generic phase diagram of heavy fermion systems, tuning an external parameter such as hydrostatic or chemical pressure modifies the superconducting transition temperature. The superconducting phase forms a dome in the temperature—tuning parameter phase diagram, which is associated with a maximum of the superconducting pairing interaction. Proximity to antiferromagnetism suggests a relation between the disappearance of antiferromagnetic order and superconductivity. We combine muon spin rotation, neutron scattering, and x-ray absorption spectroscopy techniques to gain access to the magnetic and electronic structure of CeCo(In1−xCdx)5 at different time scales. Different magnetic structures are obtained that indicate a magnetic order of itinerant character, coexisting with bulk superconductivity. The suppression of the antiferromagnetic order appears to be driven by a modification of the bandwidth/carrier concentration, implying that the electronic structure and consequently the interplay of superconductivity and magnetism is strongly affected by hydrostatic and chemical pressure. PMID:26224422

  7. Logarithmic temperature dependence of samarium ion valence in the heavy-fermion S mxL a1 -xO s4S b12

    NASA Astrophysics Data System (ADS)

    Fushiya, Kengo; Miyazaki, Ryoichi; Higashinaka, Ryuji; Yamada, Akira; Mizumaki, Masaichiro; Tsutsui, Satoshi; Nitta, Kiyofumi; Uruga, Tomoya; Suemitsu, Bunya; Sato, Hideyuki; Aoki, Yuji

    2015-08-01

    We have measured x-ray absorption spectra at the Sm L3 edge to investigate the Sm-ion valence of (S mxL a1 -x) O s4S b12 , in which field-insensitive heavy-fermion behavior appears at low temperatures for x =1 . It has been found that the Sm-ion valance shifts to 2 + with La ion substitution; from v =+2.78 (x =1 ) to v =+2.73 (x =0.2 ) at 10 K. For all x investigated, its temperature dependence shows a logT behavior, indicating that the valence change is caused by "an unconventional Kondo effect" associated with Sm 4 f -electron charge degrees of freedom. Almost x independence of "the associated Kondo temperature" (T˜K=56 ±10 K ) indicates that the Kondo effect has a local nature, attributable to the cage structure of the filled skutterudite.

  8. Evidence for Coexistence of Bulk Superconductivity and Itinerant Antiferromagnetism in the Heavy Fermion System CeCo(In(1-x)Cdx)5.

    PubMed

    Howald, Ludovic; Stilp, Evelyn; de Réotier, Pierre Dalmas; Yaouanc, Alain; Raymond, Stéphane; Piamonteze, Cinthia; Lapertot, Gérard; Baines, Christopher; Keller, Hugo

    2015-07-30

    In the generic phase diagram of heavy fermion systems, tuning an external parameter such as hydrostatic or chemical pressure modifies the superconducting transition temperature. The superconducting phase forms a dome in the temperature-tuning parameter phase diagram, which is associated with a maximum of the superconducting pairing interaction. Proximity to antiferromagnetism suggests a relation between the disappearance of antiferromagnetic order and superconductivity. We combine muon spin rotation, neutron scattering, and x-ray absorption spectroscopy techniques to gain access to the magnetic and electronic structure of CeCo(In(1-x)Cdx)5 at different time scales. Different magnetic structures are obtained that indicate a magnetic order of itinerant character, coexisting with bulk superconductivity. The suppression of the antiferromagnetic order appears to be driven by a modification of the bandwidth/carrier concentration, implying that the electronic structure and consequently the interplay of superconductivity and magnetism is strongly affected by hydrostatic and chemical pressure.

  9. Experimental study of knight shift trends in the heavy fermion compounds compounds Cerium-M-Indium5 (M=Iridium, Rhodium, Cobalt)

    NASA Astrophysics Data System (ADS)

    Shockley, Abigail Caroline

    The heavy electron Kondo liquid is an emergent state of condensed matter that displays universal behavior independent of material details. Properties of the heavy electron liquid are best probed by NMR Knight shift measurements, which provide a direct measure of the behavior of the heavy electron liquid that emerges below the Kondo lattice coherence temperature as the lattice of local moments hybridizes with the background conduction electrons. Because the transfer of spectral weight between the localized and itinerant electronic degrees of freedom is gradual, the Kondo liquid typically coexists with the local moment component until the material orders at low temperatures. The two-fluid formula captures this behavior in a broad range of materials in the paramagnetic state. In order to investigate two-fluid behavior and the onset and physical origin of different long range ordered ground states in heavy electron materials, we present Knight shift measurements in Ce1-xLaxCoIn5, CeIrIn5 and CeRhIn5. In CeRhIn5 we find that the anti-ferromagnetic order is preceded by a re-localization of the Kondo liquid, providing independent evidence for a local moment origin of anti-ferromagnetism. In CeIrIn5 we find that the relative weight of the Kondo liquid gradually changes as the sample is rotated while the coherence temperature is unaffected. At high fields around 30T, the coherence temperature in CeIrIn5 is likewise unaffected. The Kondo liquid also remains unaffected at high fields. In Ce1-xLaxCoIn5,we find that the Kondo liquid is due to short range interactions. In this work, we have also found that the two-fluid model is not always the best description of these materials.

  10. Fermion production during and after axion inflation

    SciTech Connect

    Adshead, Peter; Sfakianakis, Evangelos I.

    2015-11-11

    We study derivatively coupled fermions in axion-driven inflation, specifically m{sub ϕ}{sup 2}ϕ{sup 2} and monodromy inflation, and calculate particle production during the inflationary epoch and the post-inflationary axion oscillations. During inflation, the rolling axion acts as an effective chemical potential for helicity which biases the gravitational production of one fermion helicity over the other. This mechanism allows for efficient gravitational production of heavy fermion states that would otherwise be highly suppressed. Following inflation, the axion oscillates and fermions with both helicities are produced as the effective frequency of the fermion field changes non-adiabatically. For certain values of the fermion mass and axion-fermion coupling strength, the two helicity states are produced asymmetrically, resulting in unequal number-densities of left- and right-helicity fermions.

  11. Fermion production during and after axion inflation

    SciTech Connect

    Adshead, Peter; Sfakianakis, Evangelos I. E-mail: esfaki@illinois.edu

    2015-11-01

    We study derivatively coupled fermions in axion-driven inflation, specifically m{sub φ}{sup 2φ2} and monodromy inflation, and calculate particle production during the inflationary epoch and the post-inflationary axion oscillations. During inflation, the rolling axion acts as an effective chemical potential for helicity which biases the gravitational production of one fermion helicity over the other. This mechanism allows for efficient gravitational production of heavy fermion states that would otherwise be highly suppressed. Following inflation, the axion oscillates and fermions with both helicities are produced as the effective frequency of the fermion field changes non-adiabatically. For certain values of the fermion mass and axion-fermion coupling strength, the two helicity states are produced asymmetrically, resulting in unequal number-densities of left- and right-helicity fermions.

  12. Heavy-Fermion Valence-Bond Liquids in Ultracold Atoms: Cooperation of the Kondo Effect and Geometric Frustration.

    PubMed

    Isaev, L; Rey, A M

    2015-10-16

    We analyze a microscopic mechanism behind the coexistence of a heavy Fermi liquid and geometric frustration in Kondo lattices. We consider a geometrically frustrated periodic Anderson model and demonstrate how orbital fluctuations lead to a Kondo-screened phase in the limit of extreme strong frustration when only local singlet states participate in the low-energy physics. We also propose a setup to realize and study this exotic state with SU(3)-symmetric alkaline-earth cold atoms.

  13. Heavy-impurity resonance, hybridization, and phonon spectral functions in Fe1-xMxSi, M=Ir,Os

    DOE PAGES

    Delaire, O.; Al-Qasir, Iyad I.; May, Andrew F.; ...

    2015-03-31

    The vibrational behavior of heavy substitutional impurities (M=Ir,Os) in Fe1-xMxSi (x = 0, 0.02, 0.04, 0.1) was investigated with a combination of inelastic neutron scattering (INS), transport measurements, and first-principles simulations. In this paper, our INS measurements on single-crystals mapped the four-dimensional dynamical structure factor, S(Q;E), for several compositions and temperatures. Our results show that both Ir and Os impurities lead to the formation of a weakly dispersive resonance vibrational mode, in the energy range of the acoustic phonon dispersions of the FeSi host. We also show that Ir doping, which introduces free carriers and increases electron-phonon coupling, leads tomore » softened interatomic force-constants compared to doping with Os, which is isoelectronic to Fe. We analyze the phonon S(Q,E) from INS through a Green's function model incorporating the phonon self-energy based on first-principles density functional theory (DFT) simulations. Calculations of the quasiparticle spectral functions in the doped system reveal the hybridization between the resonance and the acoustic phonon modes. Finally, our results demonstrate a strong interaction of the host acoustic dispersions with the resonance mode, likely leading to the large observed suppression in lattice thermal conductivity.« less

  14. Heavy-impurity resonance, hybridization, and phonon spectral functions in Fe1-xMxSi (M =Ir , Os )

    NASA Astrophysics Data System (ADS)

    Delaire, O.; Al-Qasir, I. I.; May, A. F.; Li, C. W.; Sales, B. C.; Niedziela, J. L.; Ma, J.; Matsuda, M.; Abernathy, D. L.; Berlijn, T.

    2015-03-01

    The vibrational behavior of heavy substitutional impurities (M = Ir,Os) in Fe1-xMxSi (x =0 ,0.02 ,0.04 ,0.1 ) was investigated with a combination of inelastic neutron scattering (INS), transport measurements, and first-principles simulations. Our INS measurements on single crystals mapped the four-dimensional dynamical structure factor, S (Q ,E ) , for several compositions and temperatures. Our results show that both Ir and Os impurities lead to the formation of a weakly dispersive resonance vibrational mode, in the energy range of the acoustic phonon dispersions of the FeSi host. We also show that Ir doping, which introduces free carriers, leads to softened interatomic force constants compared to doping with Os, which is isoelectronic to Fe. We analyze the phonon S (Q ,E ) from INS through a Green's-function model incorporating the phonon self-energy based on first-principles density functional theory simulations, and we study the disorder-induced lifetimes on large supercells. Calculations of the quasiparticle spectral functions in the doped system reveal the hybridization between the resonance and the acoustic phonon modes. Our results demonstrate a strong interaction of the host acoustic dispersions with the resonance mode, likely leading to the large observed suppression in lattice thermal conductivity.

  15. Point Contact Spectroscopy Study of CeCoIn5: Evidence for Unconventional Pairing in a Multi-Band Heavy Fermion Superconductor

    NASA Astrophysics Data System (ADS)

    Rourke, P. M. C.; Tanatar, M. A.; Petrovic, C.; Wei, J. Y. T.

    2005-03-01

    Point-contact spectroscopy was performed on single crystals of the heavy-fermion superconductor CeCoIn5 in the temperature range 150mK to 2.5K. A pulsed measurement technique ensured minimal Joule heating over a wide voltage range. The spectra show Andreev-reflection characteristics with multiple structures which depend on junction impedance. Spectral analysis using the generalized BTK formalism revealed two nodal order-parameter components, with amplitudes δ1=0.95 ±0.15meV and δ2=2.4±0.3meV which evolve differently with temperature. These observations indicate a highly unconventional pairing mechanism, possibly involving multiple bands [1]. Measurements are also done in a magnetic field to study the field-evolution of the order-parameter components we observed. [1] P.M.C. Rourke, et al. cond-mat/0409562. Work supported by: NSERC, CFI/OIT, MMO/EMK and the Canadian Institute for Advanced Research. Work at Brookhaven supported by: Division of Materials Sciences, Office of Basic Energy Sciences, US Department of Energy under contract no. DE-AC02- 98CH10886.

  16. Magnetically Robust Non-Fermi Liquid Behavior in Heavy Fermion Systems with f2-Configuration: Competition between Crystalline-Electric-Field and Kondo-Yosida Singlets

    NASA Astrophysics Data System (ADS)

    Nishiyama, Shinya; Matsuura, Hiroyasu; Miyake, Kazumasa

    2010-10-01

    In f2-based heavy fermion systems with a crystalline-electric-field (CEF) singlet ground state, the non-Fermi liquid (NFL) arises around the quantum critical point (QCP) due to the competition between the CEF singlet and the Kondo-Yosida singlet states. In such a case, the characteristic temperature TF* at which the entropy starts to decrease toward zero is suppressed by the effect of the competition, compared to both energy scales characterizing each singlet state, the lower Kondo temperature (TK2) and the CEF splitting (Δ). We show that in the case of tetragonal symmetry TF* is not affected by the magnetic field up to Hz* which is determined by the distance from the QCP or characteristic energy scales of each singlet states, not by TF* itself. As a result, in the vicinity of QCP, there are parameter regions where the NFL is robust against the magnetic field, at an observable temperature range T > TF*, up to Hz* which is far larger than TF* and less than \\min(TK2,Δ). Our result suggests that such an anomalous NFL behavior can arise also in systems with other CEF symmetry, which might provide us with the basis to understand the anomalous behaviors of UBe13.

  17. Influence of Heavy Fermion Ytterbium Substitution on the Electronic and Crystal Properties of the Frustrated Magnet CuFeO2 Oxide

    NASA Astrophysics Data System (ADS)

    Ozkendir, Osman Murat

    2017-09-01

    The influence of heavy fermion Ytterbium substitution was investigated on the crystal, electronic, and magnetic properties of CuFeO2 with the general formula Yb x Cu1-x FeO2. The results of the crystal structure study revealed polycrystalline formations in the sample. The electronic and magnetic properties of the samples were studied using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) techniques. Both XAS and XMCD revealed that the substituted Yb atoms govern the entire phenomena with their narrow 4f levels by forming broader molecular bonds with the 3d levels of the transition metals. Owing to the prominent changes caused by the activity of the 4f electrons in the crystal structures, Yb atoms were determined to be the main "role player" in the phase transitions. XMCD measurements were performed at room temperature 300 K (27 °C) to determine the magnetic properties of the samples and, except for CuFeO2 (x = 0.0), the samples were observed to be ordered magnetically (mainly ferrimagnetic) in the bulk.

  18. Electronic structure of Ce2RhIn8: A two-dimensional heavy-fermion system studied by angle-resolved photoemission spectroscopy

    DOE PAGES

    Jiang, Rui; Mou, Daixing; Liu, Chang; ...

    2015-04-01

    We use angle-resolved photoemission spectroscopy (ARPES) to study the 2D heavy fermion superconductor, Ce₂RhIn₈. The Fermi surface is rather complicated and consists of several hole and electron pockets with one of the sheets displaying strong nesting properties with a q-vector of (0.32, 0.32) π/a. We do not observe kz dispersion of the Fermi sheets, which is consistent with the expected 2D character of the electronic structure. Comparison of the ARPES data to band structure calculations suggests that a localized picture of the f-electrons works best. While there is some agreement in the overall band dispersion and location of the Fermimore » sheets, the model does not reproduce all observed bands and is not completely accurate for those it does. As a result, our data paves the way for improving the band structure calculations and the general understanding of the transport and thermodynamical properties of this material.« less

  19. Quantum critical fluctuations in the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2

    DOE PAGES

    Wang, C. H.; Poudel, L.; Taylor, Alice E.; ...

    2014-12-03

    Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experiments were performed on a single crystal of the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2 in order to research the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ≤ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ~ T3/2 and γ(T) ~ γ0 - bT1/2). However, for 2 ≤ T ≤ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. In addition, despite the factmore » that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. In conclusion, we suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.« less

  20. Pressure-driven 4 f localized-itinerant crossover in heavy-fermion compound CeIn3: A first-principles many-body perspective

    NASA Astrophysics Data System (ADS)

    Lu, Haiyan; Huang, Li

    2016-08-01

    The localized-itinerant nature of Ce -4 f valence electrons in heavy fermion compound CeIn3 under pressure is studied thoroughly by means of the combination of density functional theory and single-site dynamical mean-field theory. The detailed evolutions of electronic structures of CeIn3, including total and partial density of states, momentum-resolved spectral functions, and valence state histograms, are calculated in a wide pressure range where the corresponding volume compression V /V0∈[0.6 ,1.0 ] (here V0 is the experimental crystal volume) at T ≅116 K. Upon increasing pressure, two strong peaks associated with the Ce -4 f states emerge near the Fermi level, and the c -f hybridization and valence state fluctuation are enhanced remarkably. Moreover, the kinetic and potential energies rise, while the occupancy, total angular momentum, and low-energy scattering rate of the Ce -4 f electrons decline with respect to pressure. All the physical observables considered here exhibit prominent kinks or fluctuations in V /V0∈[0.80 ,0.90 ] , which are probably the desired fingerprints for the Ce -4 f localized-itinerant crossover.

  1. Thermodynamic study of gap structure and pair-breaking effect by magnetic field in the heavy-fermion superconductor CeCu2Si2

    NASA Astrophysics Data System (ADS)

    Kittaka, Shunichiro; Aoki, Yuya; Shimura, Yasuyuki; Sakakibara, Toshiro; Seiro, Silvia; Geibel, Christoph; Steglich, Frank; Tsutsumi, Yasumasa; Ikeda, Hiroaki; Machida, Kazushige

    2016-08-01

    This paper presents the results of specific-heat and magnetization measurements, in particular their field-orientation dependence, on the first discovered heavy-fermion superconductor CeCu2Si2 (Tc˜0.6 K). We discuss the superconducting gap structure and the origin of the anomalous pair-breaking phenomena, leading, e.g., to the suppression of the upper critical field Hc 2, found in the high-field region. The data show that the anomalous pair breaking becomes prominent below about 0.15 K in any field direction, but occurs closer to Hc 2 for H ∥c . The presence of this anomaly is confirmed by the fact that the specific-heat and magnetization data satisfy standard thermodynamic relations. Concerning the gap structure, field-angle dependencies of the low-temperature specific heat within the a b and a c planes do not show any evidence for gap nodes. From microscopic calculations in the framework of a two-band full-gap model, the power-law-like temperature dependencies of C and 1 /T1 , reminiscent of nodal superconductivity, have been reproduced reasonably. These facts further support multiband full-gap superconductivity in CeCu2Si2 .

  2. Quasi-two-dimensional Fermi surfaces with localized f electrons in the layered heavy-fermion compound CePt2In7

    NASA Astrophysics Data System (ADS)

    Götze, K.; Krupko, Y.; Bruin, J. A. N.; Klotz, J.; Hinlopen, R. D. H.; Ota, S.; Hirose, Y.; Harima, H.; Settai, R.; McCollam, A.; Sheikin, I.

    2017-08-01

    We report measurements of the de Haas-van Alphen effect in the layered heavy-fermion compound CePt2In7 in high magnetic fields up to 35 T. Above an angle-dependent threshold field, we observed several de Haas-van Alphen frequencies originating from almost ideally two-dimensional Fermi surfaces. The frequencies are similar to those previously observed to develop only above a much higher field of 45 T, where a clear anomaly was detected and proposed to originate from a change in the electronic structure [M. M. Altarawneh et al., Phys. Rev. B 83, 081103 (2011), 10.1103/PhysRevB.83.081103]. Our experimental results are compared with band structure calculations performed for both CePt2In7 and LaPt2In7 , and the comparison suggests localized f electrons in CePt2In7 . This conclusion is further supported by comparing experimentally observed Fermi surfaces in CePt2In7 and PrPt2In7 , which are found to be almost identical. The measured effective masses in CePt2In7 are only moderately enhanced above the bare electron mass m0, from 2 m0 to 6 m0 .

  3. Quantum critical fluctuations in the heavy fermion compound Ce(Ni0.935Pd0.065)₂Ge₂.

    PubMed

    Wang, C H; Poudel, L; Taylor, A E; Lawrence, J M; Christianson, A D; Chang, S; Rodriguez-Rivera, J A; Lynn, J W; Podlesnyak, A A; Ehlers, G; Baumbach, R E; Bauer, E D; Gofryk, K; Ronning, F; McClellan, K J; Thompson, J D

    2015-01-14

    Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experiments were performed on a single crystal of the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2 in order to study the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ⩽ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ∼ T(3/2) and γ(T) ∼ γ0 - bT(1/2)). However, for 2 ⩽ T ⩽ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. Furthermore, despite the fact that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. We suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.

  4. Controllable Rashba spin-orbit interaction in artificially engineered superlattices involving the heavy-fermion superconductor CeCoIn5.

    PubMed

    Shimozawa, M; Goh, S K; Endo, R; Kobayashi, R; Watashige, T; Mizukami, Y; Ikeda, H; Shishido, H; Yanase, Y; Terashima, T; Shibauchi, T; Matsuda, Y

    2014-04-18

    By using a molecular beam epitaxy technique, we fabricate a new type of superconducting superlattices with controlled atomic layer thicknesses of alternating blocks between the heavy-fermion superconductor CeCoIn5, which exhibits a strong Pauli pair-breaking effect, and nonmagnetic metal YbCoIn5. The introduction of the thickness modulation of YbCoIn5 block layers breaks the inversion symmetry centered at the superconducting block of CeCoIn5. This configuration leads to dramatic changes in the temperature and angular dependence of the upper critical field, which can be understood by considering the effect of the Rashba spin-orbit interaction arising from the inversion symmetry breaking and the associated weakening of the Pauli pair-breaking effect. Since the degree of thickness modulation is a design feature of this type of superlattices, the Rashba interaction and the nature of pair breaking are largely tunable in these modulated superlattices with strong spin-orbit coupling.

  5. (Strongly interacting fermion system)

    SciTech Connect

    Not Available

    1990-01-01

    Research has been concentrated primarily in three areas: heavy fermions, physics of high-temperature superconductivity, and electronic properties. In heavy fermions a peak in the attenuation coefficient of ultrasound just below the superconducting transition temperature can be explained in the context of conventional (BCS) superconductivity theory by recognizing how profoundly that theory is reorganized in heavy fermion systems in which the sound velocity is comparable to electron Fermi velocity. In high-temperature superconductors there have been development of a model for magnetism in one alloy which shows unusual first-order phase transitions in a magnetic field, a possible mechanism for high-temperature superconductivity based on an electric quadrupole moment of Cu in tetragonal crystal geometry, and a neat resolution of a paradox between a theory connecting gaps in spectrum with the degeneracy of the system and a prominent current theoretical view that there is a gap and no degeneracy. It turns out there is a topological degeneracy that had not been previously recognized. In electronic structure we have shown that the finite element approach can be used for electronic systems with an efficient code using more than a half-million local basis functions. In addition, we have developed a variational principle for determining optimal meshes for solving differential equations --- such as the Schroedinger equation.

  6. Fermion Superfluidity

    NASA Technical Reports Server (NTRS)

    Strecker, Kevin; Truscott, Andrew; Partridge, Guthrie; Chen, Ying-Cheng

    2003-01-01

    Dual evaporation gives 50 million fermions at T = 0.1 T(sub F). Demonstrated suppression of interactions by coherent superposition - applicable to atomic clocks. Looking for evidence of Cooper pairing and superfluidity.

  7. Lattice fermions

    NASA Technical Reports Server (NTRS)

    Wilczek, Frank

    1987-01-01

    A simple heuristic proof of the Nielsen-Ninomaya theorem is given. A method is proposed whereby the multiplication of fermion species on a lattice is reduced to the minimal doubling, in any dimension, with retention of appropriate chiral symmetries. Also, it is suggested that use of spatially thinned fermion fields is likely to be a useful and appropriate approximation in QCD - in any case, it is a self-checking one.

  8. NMR investigation of the Knight shift anomaly in CeIrIn5 at high magnetic fields

    NASA Astrophysics Data System (ADS)

    Shockley, A. C.; apRoberts-Warren, N.; Nisson, D. M.; Kuhns, P. L.; Reyes, A. P.; Yuan, S.; Curro, N. J.

    2013-08-01

    We report nuclear magnetic resonance Knight shift data in the heavy-fermion material CeIrIn5 at fields up to 30 T. The Knight shift of the In displays a strong anomaly, and we analyze the results using two interpretations. We find that the Kondo lattice coherence temperature and the effective mass of the heavy electrons remain largely unaffected by the magnetic field, despite the fact that the Zeeman energy is of the order of the coherence temperature.

  9. Superconductivity and Non-Fermi-Liquid Behavior in the Heavy-Fermion Compound CeCo1-xNixIn5

    NASA Astrophysics Data System (ADS)

    Otaka, Ryo; Yokoyama, Makoto; Mashiko, Hiroaki; Hasegawa, Takeshi; Shimizu, Yusei; Ikeda, Yoichi; Tenya, Kenichi; Nakamura, Shota; Ueta, Daichi; Yoshizawa, Hideki; Sakakibara, Toshiro

    2016-09-01

    The effect of off-plane impurity on superconductivity and non-Fermi-liquid (NFL) behavior in the layered heavy-fermion compound CeCo1-xNixIn5 is investigated by specific heat, magnetization, and electrical resistivity measurements. These measurements reveal that the superconducting (SC) transition temperature Tc monotonically decreases from 2.3 K (x = 0) to 0.8 K (x = 0.20) with increasing x, and then the SC order disappears above x = 0.25. At the same time, the Ni substitution yields the NFL behavior at zero field for x = 0.25, characterized by the -ln T divergence in specific heat divided by temperature, Cp/T, and magnetic susceptibility, M/B. The NFL behavior in magnetic fields for x = 0.25 is quite similar to that seen at around the SC upper critical field in pure CeCoIn5, suggesting that both compounds are governed by the same antiferromagnetic quantum criticality. The resemblance of the doping effect on the SC order among Ni-, Sn-, and Pt-substituted CeCoIn5 supports the argument that the doped carriers are primarily responsible for the breakdown of the SC order. The present investigation further reveals the quantitative differences in the trends of the suppression of superconductivity between Ce(Co,Ni)In5 and the other alloys, such as the rates of decrease in Tc, dTc/dx, and specific heat jump at Tc, d(ΔCp/Tc)/dx. We suggest that the occupied positions of the doped ions play an important role in the origin of these differences.

  10. Multiband Superconductivity in Heavy Fermion Compound CePt3Si without Inversion Symmetry: An NMR Study on a High-Quality Single Crystal

    NASA Astrophysics Data System (ADS)

    Mukuda, Hidekazu; Nishide, Sachihiro; Harada, Atsushi; Iwasaki, Kaori; Yogi, Mamoru; Yashima, Mitsuharu; Kitaoka, Yoshio; Tsujino, Masahiko; Takeuchi, Tetsuya; Settai, Rikio; Ōnuki, Yoshichika; Bauer, Ernst; Itoh, Kohei M.; Haller, Eugene E.

    2009-01-01

    We report on novel superconducting characteristics of the heavy fermion (HF) superconductor CePt3Si without inversion symmetry through 195Pt-NMR study on a single crystal with Tc= 0.46 K that is lower than Tc˜ 0.75 K for polycrystals. We show that the intrinsic superconducting characteristics inherent to CePt3Si can be understood in terms of the unconventional strong-coupling state with a line-node gap below Tc= 0.46 K. The mystery about the sample dependence of Tc is explained by the fact that more or less polycrystals and single crystals inevitably contain some disordered domains, which exhibit a conventional BCS s-wave superconductivity (SC) below 0.8 K. In contrast, the Néel temperature TN˜ 2.2 K is present regardless of the quality of samples, revealing that the Fermi surface responsible for SC differ from that for the antiferromagnetic order. These unusual characteristics of CePt3Si can be also described by a multiband model; in the homogeneous domains, the coherent HF bands are responsible for the unconventional SC, whereas in the disordered domains the conduction bands existing commonly in LaPt3Si may be responsible for the conventional s-wave SC. We remark that some impurity scatterings in the disordered domains break up the 4 f-electrons-derived coherent bands but not others. In this context, the small peak in 1/T1 just below Tc reported before [Yogi et al. (2004)] is not due to a two-component order parameter composed of spin-singlet and spin-triplet Cooper pairing states, but due to the contamination of the disorder domains which are in the s-wave SC state.

  11. Investigation of the commensurate magnetic structure in the heavy-fermion compound CePt2In7 using magnetic resonant x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Gauthier, Nicolas; Wermeille, Didier; Casati, Nicola; Sakai, Hironori; Baumbach, Ryan E.; Bauer, Eric D.; White, Jonathan S.

    2017-08-01

    We investigated the magnetic structure of the heavy-fermion compound CePt2In7 below TN=5.34 (2 ) K using magnetic resonant x-ray diffraction at ambient pressure. The magnetic order is characterized by a commensurate propagation vector k1 /2=(1/2 ,1/2 ,1/2 ) with spins lying in the basal plane. Our measurements did not reveal the presence of an incommensurate order propagating along the high-symmetry directions in reciprocal space but cannot exclude other incommensurate modulations or weak scattering intensities. The observed commensurate order can be described equivalently by either a single-k structure or by a multi-k structure. Furthermore we explain how a commensurate-only ordering may explain the broad distribution of internal fields observed in nuclear quadrupolar resonance experiments [Sakai et al., Phys. Rev. B 83, 140408 (2011), 10.1103/PhysRevB.83.140408] that was previously attributed to an incommensurate order. We also report powder x-ray diffraction showing that the crystallographic structure of CePt2In7 changes monotonically with pressure up to P =7.3 GPa at room temperature. The determined bulk modulus B0=81.1 (3 ) GPa is similar to those of the Ce-115 family. Broad diffraction peaks confirm the presence of pronounced strain in polycrystalline samples of CePt2In7 . We discuss how strain effects can lead to different electronic and magnetic properties between polycrystalline and single crystal samples.

  12. Energy-scale phenomenology and pairing via resonant spin-charge motion in FeAs, CuO, heavy-fermion and other exotic superconductors

    NASA Astrophysics Data System (ADS)

    Uemura, Y. J.

    2009-10-01

    Muon spin relaxation ( μSR) studies of the “1111” and “122” FeAs systems have detected static magnetism with variably sized ordered moments in their parent compounds. The phase diagrams of FeAs, CuO, organic BEDT, A3C60 and heavy-fermion systems indicate competition between static magnetism and superconductivity, associated with first-order phase transitions at quantum phase boundaries. In both FeAs and CuO systems, the superfluid density ns/m* at T→0 exhibits a nearly linear scaling with Tc. Analogous to the roton-minimum energy scaling with the lambda transition temperature in superfluid 4He, clear scaling with Tc was also found for the energy of the magnetic resonance mode in cuprates, (Ba,K)Fe2As2, CeCoIn5 and CeCu2Si2, as well as the energy of the superconducting coherence peak observed by angle resolved photo emission (ARPES) in the cuprates near ( π,0). Both the superfluid density and the energy of these pair-non-breaking soft-mode excitations determine the superconducting Tc via phase fluctuations of condensed bosons. Combining these observations and common dispersion relations of spin and charge collective excitations in the cuprates, we propose a resonant spin-charge motion/coupling, “traffic-light resonance,” expected when the charge energy scale εF becomes comparable to the spin fluctuation energy scale ℏωSF~J, as the process which leads to pair formation in these correlated electron superconductors.

  13. Improved IR detectors to swap heavy systems for SWaP

    NASA Astrophysics Data System (ADS)

    Manissadjian, Alain; Rubaldo, Laurent; Rebeil, Yann; Kerlain, Alexandre; Brellier, Delphine; Mollard, Laurent

    2012-06-01

    Cooled IR technologies are challenged for answering new system needs like the compactness and the reduction of cryopower which is a key feature for the SWaP (Size, Weight and Power) requirements. Over the last years, SOFRADIR has improved its HgCdTe technology, with effect on dark current reduction, opening the way for High Operating Temperature (HOT) systems that can get rid of the 80K temperature constraint, and therefore releases the Stirling cooler engine power consumption. Performances of the 640×512 15μm pitch LW detector working above 100K will be presented. A compact 640×512 15μm pitch MW detector presenting high EO performance above 130K with cut-off wavelength above 5.0μm has been developed. Its different performances with respect to the market requirements for SWaP will be discussed. High performance compact systems will make no compromise on detector resolution. The pixel pitch reduction is the answer for resolution enhancement with size reduction. We will therefore also discuss the ongoing developments and market needs for SWaP systems.

  14. Hourglass fermions.

    PubMed

    Wang, Zhijun; Alexandradinata, A; Cava, R J; Bernevig, B Andrei

    2016-04-14

    Spatial symmetries in crystals may be distinguished by whether they preserve the spatial origin. Here we study spatial symmetries that translate the origin by a fraction of the lattice period, and find that these non-symmorphic symmetries protect an exotic surface fermion whose dispersion relation is shaped like an hourglass; surface bands connect one hourglass to the next in an unbreakable zigzag pattern. These 'hourglass' fermions are formed in the large-gap insulators, KHgX (X = As, Sb, Bi), which we propose as the first material class whose band topology relies on non-symmorphic symmetries. Besides the hourglass fermion, another surface of KHgX manifests a three-dimensional generalization of the quantum spin Hall effect, which has previously been observed only in two-dimensional crystals. To describe the bulk topology of non-symmorphic crystals, we propose a non-Abelian generalization of the geometric theory of polarization. Our non-trivial topology originates from an inversion of the rotational quantum numbers, which we propose as a criterion in the search for topological materials.

  15. Hourglass Fermions

    NASA Astrophysics Data System (ADS)

    Wang, Zhijun; Alexandradinata, A.; Cava, Robert J.; Bernevig, B. Andrei

    Spatial symmetries in crystals are distinguished by whether they preserve the spatial origin. We show how this basic geometric property gives rise to a new topology in band insulators. We study spatial symmetries that translate the origin by a fraction of the lattice period, and find that these nonsymmorphic symmetries protect a novel surface fermion whose dispersion is shaped like an hourglass; surface bands connect one hourglass to the next in an unbreakable zigzag pattern. These exotic fermions are materialized in the large-gap insulators: KHg X (X = As,Sb,Bi), which we propose as the first material class whose topology relies on nonsymmorphic symmetries. Beside the hourglass fermion, a different surface of KHg X manifests a 3D generalization of the quantum spin Hall effect. To describe the bulk topology of nonsymmorphic crystals, we propose a non-Abelian generalization of the geometric theory of polarization. Our nontrivial topology originates not from an inversion of the parity quantum numbers, but rather of the rotational quantum numbers, which we propose as a fruitful in the search for topological materials. Finally, KHg X uniquely exemplifies a cohomological insulator, a concept that we will introduce in a companion work.

  16. Resistance minimum and heavy fermions

    PubMed Central

    Jun, Kondo

    2006-01-01

    The phenomenon of the resistance minimum in dilute magnetic alloys is explained in terms of the s-d interaction which takes account of scattering of the conduction electron off the magnetic impurities in metals. Some of the intermetallic compounds which involve rare earth elements or uranium show a very large electronic specific heat and remain non-magnetic even though they show a Curie-like susceptibility at higher temperatures. These phenomena are also explained based on the s-d interaction model. PMID:25792794

  17. Fermion masses through four-fermion condensates

    SciTech Connect

    Ayyar, Venkitesh; Chandrasekharan, Shailesh

    2016-10-12

    Fermion masses can be generated through four-fermion condensates when symmetries prevent fermion bilinear condensates from forming. This less explored mechanism of fermion mass generation is responsible for making four reduced staggered lattice fermions massive at strong couplings in a lattice model with a local four-fermion coupling. The model has a massless fermion phase at weak couplings and a massive fermion phase at strong couplings. In particular there is no spontaneous symmetry breaking of any lattice symmetries in both these phases. Recently it was discovered that in three space-time dimensions there is a direct second order phase transition between the two phases. Here we study the same model in four space-time dimensions and find results consistent with the existence of a narrow intermediate phase with fermion bilinear condensates, that separates the two asymptotic phases by continuous phase transitions.

  18. Fermion masses through four-fermion condensates

    DOE PAGES

    Ayyar, Venkitesh; Chandrasekharan, Shailesh

    2016-10-12

    Fermion masses can be generated through four-fermion condensates when symmetries prevent fermion bilinear condensates from forming. This less explored mechanism of fermion mass generation is responsible for making four reduced staggered lattice fermions massive at strong couplings in a lattice model with a local four-fermion coupling. The model has a massless fermion phase at weak couplings and a massive fermion phase at strong couplings. In particular there is no spontaneous symmetry breaking of any lattice symmetries in both these phases. Recently it was discovered that in three space-time dimensions there is a direct second order phase transition between the twomore » phases. Here we study the same model in four space-time dimensions and find results consistent with the existence of a narrow intermediate phase with fermion bilinear condensates, that separates the two asymptotic phases by continuous phase transitions.« less

  19. Phase transitions in the hard-core Bose-Fermi-Hubbard model at non-zero temperatures in the heavy-fermion limit

    NASA Astrophysics Data System (ADS)

    Stasyuk, I. V.; Krasnov, V. O.

    2017-04-01

    Phase transitions at non-zero temperatures in ultracold Bose- and Fermi-particles mixture in optical lattices using the Bose-Fermi-Hubbard model in the mean field and hard-core boson approximations are investigated. The case of infinitely small fermion transfer and the repulsive on-site boson-fermion interaction is considered. The possibility of change of order (from the 2nd to the 1st one) of the phase transition to the superfluid phase in the regime of fixed values of the chemical potentials of Bose- and Fermi-particles is established. The relevant phase diagrams determining the conditions at which such a change takes place, are built.

  20. Robust upward dispersion of the neutron spin resonance in the heavy fermion superconductor Ce1–xYbxCoIn5

    SciTech Connect

    Song, Yu; Van Dyke, John; Lum, I. K.; White, B. D.; Jang, Sooyoung; Yazici, Duygu; Shu, L.; Schneidewind, A.; Čermák, Petr; Qiu, Y.; Maple, M. B.; Morr, Dirk K.; Dai, Pengcheng

    2016-09-28

    Here, the neutron spin resonance is a collective magnetic excitation that appears in copper oxide, iron pnictide, and heavy fermion unconventional superconductors. Although the resonance is commonly associated with a spin-exciton due to the d(s±)-wave symmetry of the superconducting order parameter, it has also been proposed to be a magnon-like excitation appearing in the superconducting state. Here we use inelastic neutron scattering to demonstrate that the resonance in the heavy fermion superconductor Ce1–xYbxCoIn5 with x=0,0.05,0.3 has a ring-like upward dispersion that is robust against Yb-doping. By comparing our experimental data with random phase approximation calculation using the electronic structure and the momentum dependence of the dx2–y2-wave superconducting gap determined from scanning tunneling microscopy for CeCoIn5, we conclude the robust upward dispersing resonance mode in Ce1–xYbxCoIn5 is inconsistent with the downward dispersion predicted within the spin-exciton scenari

  1. The Categorification of Fermions

    NASA Astrophysics Data System (ADS)

    Wang, Na; Wang, Rui; Wang, Zhi-Xi; Wu, Ke; Yang, Jie; Yang, Zi-Feng

    2015-02-01

    In this paper, we lift Fermions to functors acting on some homotopy category by the Boson-Fermion correspondence and get the categorified relations of Fermions. In this way, both the categorified Bosons and the categorified Fermions can be viewed as functors on the same category. We also give actions of these functors on the charged Young diagrams (or equivalently Maya diagrams), so that the classical theory of Boson-Fermion correspondence is very well recovered as a result of such a categorification.

  2. Surface properties of pulsed laser deposited Ir, Rh, and Ir 0.9Rh 0.1 thin films for use as microelectrode arrays in electroanalytical heavy metal trace sensors

    NASA Astrophysics Data System (ADS)

    Le Drogoff, B.; El Khakani, M. A.; Silva, P. R. M.; Chaker, M.; Ross, G. G.

    1999-11-01

    Pulsed laser deposition (PLD) of iridium, rhodium, and Ir 0.9Rh 0.1 thin films onto a-SiC:H-coated silicon substrates for use in heavy metal sensors has been achieved by ablating iridium and/or rhodium targets with a KrF excimer laser. The deposited films are polycrystalline and exhibited very smooth surfaces with an average roughness value ( Ra) of ˜1 nm. The wettability by mercury of their surface was investigated by means of the contact angle measurement technique, and compared to that of Ag and Pt films. The PLD films (whether Ir, Rh, or Ir 0.9Rh 0.1) were found to present an almost identical Hg-wetting behavior, which is characterized by a high static contact angle of 132±2°. Moreover, in contrast to the cases of Pt or Ag films, where amalgamation with Hg rapidly occurs during the contact angle measurements, no evident interaction of Hg with the surface of the PLD films was observed. Microelectrode arrays of each of the three films (Ir, Rh and Ir 0.9Rh 0.1) were fabricated and used as a conducting base onto which Hg microdrops are electroplated. Reproducible and uniform Hg deposits on the microelectrode arrays were obtained. The electroanalytical performance of these Hg-electroplated microelectrode arrays based sensors was then evaluated by means of Square Wave Anodic Stripping Voltammetry (SWASV), in synthetic solutions containing Zn, Cd and Pb ion traces. Over a concentration range as wide as 0.2-20 ppb, the detected signals are found to exhibit a strong linear correlation with ion concentration. For a preconcentration time of only 5 min, detection limits as low as 0.2 ppb for both Cd and Pb, and 0.5 ppb for Zn were achieved.

  3. CeCu{sub 4}A{ell} and CeCu{sub 2}Zn{sub 2}A{ell}: Very heavy fermion systems in high magnetic fields

    SciTech Connect

    Andraka, B.; Kim, J.S.; Stewart, G.R. |; Fisk, Z.

    1990-12-31

    CeCu{sub 4}A{ell} and CeCu{sub 2}Zn{sub 2}A{ell} are heavy fermion systems with extremely enhanced C/T (specific heat divided by temperature) values of 2.3 and 1.8 J/K{sup 2} respectively as T {yields} 0 K. The field dependence of the low temperature specific heat is also extreme; 11 T reduces C of CeCu{sub 4}A{ell} by more than a factor of five, 12.5 T suppresses C of CeCu{sub 2}Zn{sub 2}A{ell} about seven times. Magnetic field caused changes of the specific heat of CeCu{sub 4}A{ell} are consistent with a single ion Kondo model. Magnetic correlations are at least partially responsible for the enhanced low temperature specific heat of CeCu{sub 2}Zn{sub 2}A{ell}.

  4. Effect of Pressure on Valence and Structural Properties of YbFe 2 Ge 2 Heavy Fermion Compound—A Combined Inelastic X-ray Spectroscopy, X-ray Diffraction, and Theoretical Investigation

    DOE PAGES

    Kumar, Ravhi S.; Svane, Axel; Vaitheeswaran, Ganapathy; ...

    2015-10-19

    We measured the crystal structure and the Yb valence of the YbFe2Ge2 heavy fermion compound at room temperature and under high pressures using high-pressure powder X-ray diffraction and X-ray absorption spectroscopy via both partial fluorescence yield and resonant inelastic X-ray emission techniques. Moreover, the measurements are complemented by first-principles density functional theoretical calculations using the self-interaction corrected local spin density approximation investigating in particular the magnetic structure and the Yb valence. Finally, while the ThCr2Si2-type tetragonal (I4/mmm) structure is stable up to 53 GPa, the X-ray emission results show an increase of the Yb valence from v = 2.72(2) atmore » ambient pressure to v = 2.93(3) at ~9 GPa, where at low temperature a pressure-induced quantum critical state was reported.« less

  5. Effect of Pressure on Valence and Structural Properties of YbFe2Ge2 Heavy Fermion Compound A Combined Inelastic X-ray Spectroscopy, X-ray Diffraction, and Theoretical Investigation

    SciTech Connect

    Kumar, Ravhi S.; Svane, Axel; Vaitheeswaran, Ganapathy; Kanchana, Venkatakrishnan; Antonio, Daniel; Cornelius, Andrew L.; Bauer, Eric D.; Xiao, Yuming; Chow, Paul

    2016-06-03

    The crystal structure and the Yb valence of the YbFe2Ge2 heavy fermion compound was measured at room temperature and under high pressures using high-pressure powder X-ray diffraction and X-ray absorption spectroscopy via both partial fluorescence yield and resonant inelastic X-ray emission techniques. Furthermore, the measurements are complemented by first-principles density functional theoretical calculations using the self-interaction corrected local spin density approximation investigating in particular the magnetic structure and the Yb valence. While the ThCr2Si2-type tetragonal (I4/mmm) structure is stable up to 53 GPa, the X-ray emission results show an increase of the Yb valence from v = 2.72(2) at ambient pressure to v = 2.93(3) at ~9 GPa, where at low temperature a pressure-induced quantum critical state was reported.

  6. Effect of Pressure on Valence and Structural Properties of YbFe2Ge2 Heavy Fermion Compound--A Combined Inelastic X-ray Spectroscopy, X-ray Diffraction, and Theoretical Investigation.

    PubMed

    Kumar, Ravhi S; Svane, Axel; Vaitheeswaran, Ganapathy; Kanchana, Venkatakrishnan; Antonio, Daniel; Cornelius, Andrew L; Bauer, Eric D; Xiao, Yuming; Chow, Paul

    2015-11-02

    The crystal structure and the Yb valence of the YbFe2Ge2 heavy fermion compound was measured at room temperature and under high pressures using high-pressure powder X-ray diffraction and X-ray absorption spectroscopy via both partial fluorescence yield and resonant inelastic X-ray emission techniques. The measurements are complemented by first-principles density functional theoretical calculations using the self-interaction corrected local spin density approximation investigating in particular the magnetic structure and the Yb valence. While the ThCr2Si2-type tetragonal (I4/mmm) structure is stable up to 53 GPa, the X-ray emission results show an increase of the Yb valence from v = 2.72(2) at ambient pressure to v = 2.93(3) at ∼9 GPa, where at low temperature a pressure-induced quantum critical state was reported.

  7. Dynamical symmetries for fermions

    SciTech Connect

    Guidry, M.

    1989-01-01

    An introduction is given to the Fermion Dynamical Symmetry Model (FDSM). The analytical symmetry limits of the model are then applied to the calculation of physical quantities such as ground-state masses and B(E{sub 2}) values in heavy nuclei. These comparisons with data provide strong support for a new principle of collective motion, the Dynamical Pauli Effect, and suggest that dynamical symmetries which properly account for the pauli principle are much more persistent in nuclear structure than the corresponding boson symmetries. Finally, we present an assessment of criticisms which have been voiced concerning the FDSM, and a discussion of new phenomena and exotic spectroscopy'' which may be suggested by the model. 14 refs., 8 figs., 4 tabs.

  8. Quantum critical behavior in an antiferromagnetic heavy-fermion Kondo lattice system (Ce{}_{1-x}La x )2Ir3Ge5

    NASA Astrophysics Data System (ADS)

    Khan, Rajwali; Mao, Qianhui; Wang, Hangdong; Yang, Jinhu; Du, Jianhua; Xu, Binjie; Zhou, Yuxing; Zhang, Yannan; Chen, Bing; Fang, Minghu

    2017-01-01

    Not Available Project supported by the National Basic Research Program of China (Grant Nos. 2016FYA0300402, 2015CB921004, and 2012CB821404) and the National Natural Science Foundation of China (Grant Nos. 11374261 and 11204059).

  9. Chiral fermions in asymptotically safe quantum gravity.

    PubMed

    Meibohm, J; Pawlowski, J M

    2016-01-01

    We study the consistency of dynamical fermionic matter with the asymptotic safety scenario of quantum gravity using the functional renormalisation group. Since this scenario suggests strongly coupled quantum gravity in the UV, one expects gravity-induced fermion self-interactions at energies of the Planck scale. These could lead to chiral symmetry breaking at very high energies and thus to large fermion masses in the IR. The present analysis which is based on the previous works (Christiansen et al., Phys Rev D 92:121501, 2015; Meibohm et al., Phys Rev D 93:084035, 2016), concludes that gravity-induced chiral symmetry breaking at the Planck scale is avoided for a general class of NJL-type models. We find strong evidence that this feature is independent of the number of fermion fields. This finding suggests that the phase diagram for these models is topologically stable under the influence of gravitational interactions.

  10. Chiral fermions in asymptotically safe quantum gravity

    NASA Astrophysics Data System (ADS)

    Meibohm, J.; Pawlowski, J. M.

    2016-05-01

    We study the consistency of dynamical fermionic matter with the asymptotic safety scenario of quantum gravity using the functional renormalisation group. Since this scenario suggests strongly coupled quantum gravity in the UV, one expects gravity-induced fermion self-interactions at energies of the Planck scale. These could lead to chiral symmetry breaking at very high energies and thus to large fermion masses in the IR. The present analysis which is based on the previous works (Christiansen et al., Phys Rev D 92:121501, 2015; Meibohm et al., Phys Rev D 93:084035, 2016), concludes that gravity-induced chiral symmetry breaking at the Planck scale is avoided for a general class of NJL-type models. We find strong evidence that this feature is independent of the number of fermion fields. This finding suggests that the phase diagram for these models is topologically stable under the influence of gravitational interactions.

  11. Magnetic fluctuations and possible formation of a spin-singlet cluster under pressure in the heavy-fermion spinel LiV2O4 probed by 7Li and 51V NMR

    NASA Astrophysics Data System (ADS)

    Takeda, Hikaru; Kato, Yusuke; Yoshimura, Masahiro; Shimizu, Yasuhiro; Itoh, Masayuki; Niitaka, Seiji; Takagi, Hidenori

    2015-07-01

    7Li and 51V NMR measurements up to 9.8 GPa have been made to elucidate local magnetic properties of a heavy-fermion spinel oxide LiV2O4 which undergoes a metal-insulator transition above ˜7 GPa. The temperature T and pressure P dependences of the 7Li and 51V Knight shifts and the nuclear spin-lattice relaxation rates 1 /T1 show that in the metallic phase, there is a crossover from a high-T region with weak ferromagnetic fluctuations to a low-T one with antiferromagnetic (AFM) fluctuations. The AFM fluctuations are enhanced below 20 K and 1.5 GPa, where a heavy Fermi-liquid state with the modified Korringa relation is formed. The evolution of the magnetic fluctuations is discussed from the aspect of the competition among several magnetic interactions. Above PMI˜6.7 GPa, we find the coexistence of metallic and insulating phases due to the first-order metal-insulator transition. The 7Li and 51V NMR spectra coming from the insulating phase have T -independent small Knight shifts and 7(1 /T1 ) with the thermally activated T dependence, indicating the formation of a spin-singlet cluster. We propose a model of a spin-singlet tetramer as discussed in geometrically frustrated materials.

  12. Two-gluon correlations in heavy-light ion collisions: Energy and geometry dependence, IR divergences, and kT-factorization

    NASA Astrophysics Data System (ADS)

    Kovchegov, Yuri V.; Wertepny, Douglas E.

    2014-05-01

    We study the properties of the cross section for two-gluon production in heavy-light ion collisions derived in our previous paper [1] in the saturation/Color Glass Condensate framework. Concentrating on the energy and geometry dependence of the corresponding correlation functions we find that the two-gluon correlator is a much slower function of the center-of-mass energy than the one- and two-gluon production cross sections. The geometry dependence of the correlation function leads to stronger azimuthal near- and away-side correlations in the tip-on-tip U+U collisions than in the side-on-side U+U collisions, an exactly opposite behavior from the correlations generated by the elliptic flow of the quark-gluon plasma: a study of azimuthal correlations in the U+U collisions may thus help to disentangle the two sources of correlations. We demonstrate that the cross section for two-gluon production in heavy-light ion collisions contains a power-law infrared (IR) divergence even for fixed produced gluon momenta: while saturation effects in the target regulate some of the power-law IR-divergent terms in the lowest-order expression for the two-gluon correlator, other power-law IR-divergent terms remain, possibly due to absence of saturation effects in the dilute projectile. Finally we rewrite our result for the two-gluon production cross-section in a kT-factorized form, obtaining a new factorized expression involving a convolution of one- and two-gluon Wigner distributions over both the transverse momenta and impact parameters. We show that the two-gluon production cross-section depends on two different types of unintegrated two-gluon Wigner distribution functions.

  13. Heavy-impurity resonance, hybridization, and phonon spectral functions in Fe1-xMxSi, M=Ir,Os

    SciTech Connect

    Delaire, O.; Al-Qasir, Iyad I.; May, Andrew F.; Sales, Brian C.; Niedziela, Jennifer L.; Ma, Jie; Matsuda, Masaaki; Abernathy, Douglas L.; Berlijn, Tom

    2015-03-31

    The vibrational behavior of heavy substitutional impurities (M=Ir,Os) in Fe1-xMxSi (x = 0, 0.02, 0.04, 0.1) was investigated with a combination of inelastic neutron scattering (INS), transport measurements, and first-principles simulations. In this paper, our INS measurements on single-crystals mapped the four-dimensional dynamical structure factor, S(Q;E), for several compositions and temperatures. Our results show that both Ir and Os impurities lead to the formation of a weakly dispersive resonance vibrational mode, in the energy range of the acoustic phonon dispersions of the FeSi host. We also show that Ir doping, which introduces free carriers and increases electron-phonon coupling, leads to softened interatomic force-constants compared to doping with Os, which is isoelectronic to Fe. We analyze the phonon S(Q,E) from INS through a Green's function model incorporating the phonon self-energy based on first-principles density functional theory (DFT) simulations. Calculations of the quasiparticle spectral functions in the doped system reveal the hybridization between the resonance and the acoustic phonon modes. Finally, our results demonstrate a strong interaction of the host acoustic dispersions with the resonance mode, likely leading to the large observed suppression in lattice thermal conductivity.

  14. Magnetically robust non-fermi liquid behavior due to the competition between crystalline-electric field singlet and Kondo-Yosida singlet in f2-based heavy fermion systems

    NASA Astrophysics Data System (ADS)

    Nishiyama, Shinya; Matsuura, Hiroyasu; Miyake, Kazumasa

    2011-01-01

    In f2-based heavy fermion systems with a tetragonal symmetry, we investigate the magnetic field dependence of a non-fermi liquid (NFL) which arises related to the quantum critical point (QCP) due to the competition between the crystalline-electric field (CEF) singlet and the Kondo-Yosida singlet states. On the basis of the Wilson numerical renormalization group method, we find that the magnetic field less than a characteristic magnetic field Hz* does not affect the characteristic temperature TF* at which the specific heat takes a maximum value. Since such Hz* increases as the deviation from the QCP increases, slightly off the QCP, there are parameter regions where NFL behaviors are robust at an observable temperature range T > TF*against a magnetic field of up to Hz* which is far larger than TF*. Our result suggests that such robust NFL behaviors can arise also in systems with other CEF symmetries; e.g., magnetically robust NFL behaviors observed in UBe13 may be understood on this basis.

  15. Quantum critical fluctuations in the heavy fermion compound Ce(Ni0.935 Pd0.065)2Ge2

    SciTech Connect

    Wang, C. H.; Poudel, L.; Taylor, A. E.; Lawrence, J. M.; Christianson, A. D.; Chang, S.; Rodriguez-Rivera, J. A.; Lynn, J. W.; Podlesnyak, A. A.; Ehlers, G.; Baumbach, R. E.; Bauer, E. D.; Gofryk, K.; Ronning, F.; McClellan, K. J.; Thompson, J. D.

    2015-01-14

    Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experi- ments were performed on a single crystal of the heavy fermion compound Ce(Ni0.935 Pd0.065)2Ge2 in order to study the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ≤ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ~ T3/2 and γ(T) ~ γ0 - bT1/2). However, for 2 ≤ T ≤ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. Furthermore, despite the fact that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. We suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.

  16. Quantum critical fluctuations in the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2

    SciTech Connect

    Wang, C. H.; Poudel, L.; Taylor, Alice E.; Lawrence, J M.; Christianson, Andrew D.; Chang, S.; Rodriguez-Rivera, J. A.; Lynn, J. W.; Podlesnyak, Andrey A.; Ehlers, G.; Baumbach, R. E.; Bauer, E. D.; Gofryk, Krzysztof; Ronning, F.; Mcclellan, K. J.; Thompson, J. D.

    2014-12-03

    Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experiments were performed on a single crystal of the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2 in order to research the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ≤ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ~ T3/2 and γ(T) ~ γ0 - bT1/2). However, for 2 ≤ T ≤ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. In addition, despite the fact that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. In conclusion, we suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.

  17. High pressure effects on U L 3 x-ray absorption in partial fluorescence yield mode and single crystal x-ray diffraction in the heavy fermion compound UCd 11

    DOE PAGES

    Nasreen, Farzana; Antonio, Daniel; VanGennep, Derrick; ...

    2016-02-15

    © 2016 IOP Publishing Ltd. We report a study of high pressure x-ray absorption (XAS) performed in the partial fluorescence yield mode (PFY) at the U L 3 edge (0-28.2 GPa) and single crystal x-ray diffraction (SXD) (0-20 GPa) on the UCd 11 heavy fermion compound at room temperature. Under compression, the PFY-XAS results show that the white line is shifted by +4.1(3) eV at the highest applied pressure of 28.2 GPa indicating delocalization of the 5f electrons. The increase in full width at half maxima and decrease in relative amplitude of the white line with respect to the edgemore » jump point towards 6d band broadening under high pressure. A bulk modulus of K 0 = 62(1) GPa and its pressure derivative, = 4.9(2) was determined from high pressure SXD results. Both the PFY-XAS and diffraction results do not show any sign of a structural phase transition in the applied pressure range.« less

  18. High pressure effects on U L 3 x-ray absorption in partial fluorescence yield mode and single crystal x-ray diffraction in the heavy fermion compound UCd 11

    SciTech Connect

    Nasreen, Farzana; Antonio, Daniel; VanGennep, Derrick; Booth, Corwin H.; Kothapalli, Karunakar; Bauer, Eric D.; Sarrao, John L.; Lavina, Barbara; Iota-Herbei, Valentin; Sinogeikin, Stanislav; Chow, Paul; Xiao, Yuming; Zhao, Yusheng; Cornelius, Andrew L.

    2016-02-15

    © 2016 IOP Publishing Ltd. We report a study of high pressure x-ray absorption (XAS) performed in the partial fluorescence yield mode (PFY) at the U L 3 edge (0-28.2 GPa) and single crystal x-ray diffraction (SXD) (0-20 GPa) on the UCd 11 heavy fermion compound at room temperature. Under compression, the PFY-XAS results show that the white line is shifted by +4.1(3) eV at the highest applied pressure of 28.2 GPa indicating delocalization of the 5f electrons. The increase in full width at half maxima and decrease in relative amplitude of the white line with respect to the edge jump point towards 6d band broadening under high pressure. A bulk modulus of K 0 = 62(1) GPa and its pressure derivative, = 4.9(2) was determined from high pressure SXD results. Both the PFY-XAS and diffraction results do not show any sign of a structural phase transition in the applied pressure range.

  19. High pressure effects on U L3 x-ray absorption in partial fluorescence yield mode and single crystal x-ray diffraction in the heavy fermion compound UCd11

    NASA Astrophysics Data System (ADS)

    Nasreen, Farzana; Antonio, Daniel; VanGennep, Derrick; Booth, Corwin H.; Kothapalli, Karunakar; Bauer, Eric D.; Sarrao, John L.; Lavina, Barbara; Iota-Herbei, Valentin; Sinogeikin, Stanislav; Chow, Paul; Xiao, Yuming; Zhao, Yusheng; Cornelius, Andrew L.

    2016-03-01

    We report a study of high pressure x-ray absorption (XAS) performed in the partial fluorescence yield mode (PFY) at the U L3 edge (0-28.2 GPa) and single crystal x-ray diffraction (SXD) (0-20 GPa) on the UCd11 heavy fermion compound at room temperature. Under compression, the PFY-XAS results show that the white line is shifted by  +4.1(3) eV at the highest applied pressure of 28.2 GPa indicating delocalization of the 5f electrons. The increase in full width at half maxima and decrease in relative amplitude of the white line with respect to the edge jump point towards 6d band broadening under high pressure. A bulk modulus of K 0  =  62(1) GPa and its pressure derivative, K0\\prime   =  4.9(2) was determined from high pressure SXD results. Both the PFY-XAS and diffraction results do not show any sign of a structural phase transition in the applied pressure range.

  20. High pressure effects on U L3 x-ray absorption in partial fluorescence yield mode and single crystal x-ray diffraction in the heavy fermion compound UCd11.

    PubMed

    Nasreen, Farzana; Antonio, Daniel; VanGennep, Derrick; Booth, Corwin H; Kothapalli, Karunakar; Bauer, Eric D; Sarrao, John L; Lavina, Barbara; Iota-Herbei, Valentin; Sinogeikin, Stanislav; Chow, Paul; Xiao, Yuming; Zhao, Yusheng; Cornelius, Andrew L

    2016-03-16

    We report a study of high pressure x-ray absorption (XAS) performed in the partial fluorescence yield mode (PFY) at the U L3 edge (0–28.2 GPa) and single crystal x-ray diffraction (SXD) (0–20 GPa) on the UCd11 heavy fermion compound at room temperature. Under compression, the PFY-XAS results show that the white line is shifted by +4.1(3) eV at the highest applied pressure of 28.2 GPa indicating delocalization of the 5f electrons. The increase in full width at half maxima and decrease in relative amplitude of the white line with respect to the edge jump point towards 6d band broadening under high pressure. A bulk modulus of K0 = 62(1) GPa and its pressure derivative, K0 = 4.9(2) was determined from high pressure SXD results. Both the PFY-XAS and diffraction results do not show any sign of a structural phase transition in the applied pressure range.

  1. Effect of Pressure on Valence and Structural Properties of YbFe 2 Ge 2 Heavy Fermion Compound—A Combined Inelastic X-ray Spectroscopy, X-ray Diffraction, and Theoretical Investigation

    SciTech Connect

    Kumar, Ravhi S.; Svane, Axel; Vaitheeswaran, Ganapathy; Kanchana, Venkatakrishnan; Antonio, Daniel; Cornelius, Andrew L.; Bauer, Eric D.; Xiao, Yuming; Chow, Paul

    2015-10-19

    We measured the crystal structure and the Yb valence of the YbFe2Ge2 heavy fermion compound at room temperature and under high pressures using high-pressure powder X-ray diffraction and X-ray absorption spectroscopy via both partial fluorescence yield and resonant inelastic X-ray emission techniques. Moreover, the measurements are complemented by first-principles density functional theoretical calculations using the self-interaction corrected local spin density approximation investigating in particular the magnetic structure and the Yb valence. Finally, while the ThCr2Si2-type tetragonal (I4/mmm) structure is stable up to 53 GPa, the X-ray emission results show an increase of the Yb valence from v = 2.72(2) at ambient pressure to v = 2.93(3) at ~9 GPa, where at low temperature a pressure-induced quantum critical state was reported.

  2. Global analysis of fermion mixing with exotics

    NASA Technical Reports Server (NTRS)

    Nardi, Enrico; Roulet, Esteban; Tommasini, Daniele

    1991-01-01

    The limits are analyzed on deviation of the lepton and quark weak-couplings from their standard model values in a general class of models where the known fermions are allowed to mix with new heavy particles with exotic SU(2) x U(1) quantum number assignments (left-handed singlets or right-handed doublets). These mixings appear in many extensions of the electroweak theory such as models with mirror fermions, E(sub 6) models, etc. The results update previous analyses and improve considerably the existing bounds.

  3. Quantum Theory of Fermion Production after Inflation

    NASA Astrophysics Data System (ADS)

    Berges, Jürgen; Gelfand, Daniil; Pruschke, Jens

    2011-08-01

    We show that quantum effects dramatically enhance the production of fermions following preheating after inflation in the early Universe in the presence of high excitations of bosonic quanta. As a consequence, fermions rapidly approach a quasistationary distribution with a thermal occupancy in the infrared, while the inflaton enters a turbulent scaling regime. The failure of standard semiclassical descriptions based on the Dirac equation with a homogeneous background field is caused by nonperturbatively high boson occupation numbers. During preheating the inflaton occupation number increases, thus leading to a dynamical mechanism for the enhanced production of fermions from the rescattering of the inflaton quanta. We comment on related phenomena in heavy-ion collisions for the production of quark matter fields from highly occupied gauge bosons.

  4. SU(3) sextet model with Wilson fermions

    NASA Astrophysics Data System (ADS)

    Hansen, Martin; Drach, Vincent; Pica, Claudio

    2017-08-01

    We investigate the spectrum and IR properties of the SU(3) "sextet" model with two Dirac fermions in the two-index symmetric representation via lattice simulations. This model is a prime candidate for a realization of walking technicolor, which features a minimal matter content and it is expected to be inside or very close to the lower boundary of the conformal window. We use the Wilson discretization for the fermions and map the phase structure of the lattice model. We study several spectral and gradient flow observables both in the bulk and the weak coupling phases. While in the bulk phase we find clear signs of chiral symmetry breaking, in the weak coupling phase there is no clear indication for it, and instead the chiral limit of the model seems compatible with an IR-conformal behavior.

  5. Quadrupole-driven non-Fermi-liquid and magnetic-field-induced heavy fermion states in a non-Kramers doublet system

    NASA Astrophysics Data System (ADS)

    Onimaru, T.; Izawa, K.; Matsumoto, K. T.; Yoshida, T.; Machida, Y.; Ikeura, T.; Wakiya, K.; Umeo, K.; Kittaka, S.; Araki, K.; Sakakibara, T.; Takabatake, T.

    2016-08-01

    Orbital degrees of freedom in condensed matter could play important roles in forming a variety of exotic electronic states by interacting with conduction electrons. In 4 f -electron systems, because of strong intra-atomic spin-orbit coupling, an orbitally degenerate state inherently carries quadrupolar degrees of freedom. The present work has focused on a purely quadrupole-active system PrIr2Zn20 showing superconductivity in the presence of an antiferroquadrupole order at TQ=0.11 K. We observed non-Fermi-liquid (NFL) behaviors emerging in the electrical resistivity ρ and the 4 f contribution to the specific heat, C4 f, in the paramagnetic state at T > TQ. Moreover, in magnetic fields B ≤6 T, all data sets of ρ (T ) and C4 f(T ) are well scaled with characteristic temperatures T0's. This observation of the NFL state in the nonmagnetic quadrupole-active system has an origin intrinsically different from that observed in the vicinity of the conventional quantum critical point. It implies possible formation of a quadrupole Kondo lattice resulting from hybridization between the quadrupoles and the conduction electrons with an energy scale of kBT0 . At T ≤0.13 K, ρ (T ) and C4 f(T ) exhibit anomalies as B approaches 5 T. This is the manifestation of a field-induced crossover toward a Fermi-liquid ground state in the quadrupole Kondo lattice.

  6. Magnetic, electrical, and thermodynamic properties of NpIr: Ambient and high-pressure measurements, and electronic structure calculations

    NASA Astrophysics Data System (ADS)

    Walker, H. C.; McEwen, K. A.; Griveau, J.-C.; Eloirdi, R.; Amador, P.; Maldonado, P.; Oppeneer, P. M.; Colineau, E.

    2015-05-01

    We present bulk property measurements of NpIr, a newly synthesized member of the Np-Ir binary phase diagram, which is isostructural to the noncentrosymmetric pressure-induced ferromagnetic superconductor UIr. Magnetic susceptibility, electronic transport properties at ambient and high pressure, and heat capacity measurements have been performed for temperatures T =0.55 -300 K in a range of magnetic fields up to 14 T and under pressure up to 17.3 GPa. These reveal that NpIr is a moderately heavy fermion Kondo system with strong antiferromagnetic interactions, but there is no evidence of any phase transition down to 0.55 K or at the highest pressure achieved. Experimental results are compared with ab initio calculations of the electronic band structure and lattice heat capacity. An extremely low lattice thermal conductivity is predicted for NpIr at temperatures above 300 K.

  7. Entanglement in fermionic systems

    SciTech Connect

    Banuls, Mari-Carmen; Cirac, J. Ignacio; Wolf, Michael M.

    2007-08-15

    The anticommuting properties of fermionic operators, together with the presence of parity conservation, affect the concept of entanglement in a composite fermionic system. Hence different points of view can give rise to different reasonable definitions of separable and entangled states. Here we analyze these possibilities and the relationship between the different classes of separable states. The behavior of the various classes when taking multiple copies of a state is also studied, showing that some of the differences vanish in the asymptotic regime. In particular, in the case of only two fermionic modes all the classes become equivalent in this limit. We illustrate the differences and relations by providing a complete characterization of all the sets defined for systems of two fermionic modes. The results are applied to Gibbs states of infinite chains of fermions whose interaction corresponds to a XY Hamiltonian with transverse magnetic field.

  8. Omnidirectional Measurements of Angle-Resolved Heat Capacity for Complete Detection of Superconducting Gap Structure in the Heavy-Fermion Antiferromagnet UPd_{2}Al_{3}.

    PubMed

    Shimizu, Yusei; Kittaka, Shunichiro; Sakakibara, Toshiro; Tsutsumi, Yasumasa; Nomoto, Takuya; Ikeda, Hiroaki; Machida, Kazushige; Homma, Yoshiya; Aoki, Dai

    2016-07-15

    Quasiparticle excitations in UPd_{2}Al_{3} were studied by means of heat-capacity (C) measurements under rotating magnetic fields using a high-quality single crystal. The field dependence shows C(H)∝H^{1/2}-like behavior at low temperatures for both two hexagonal crystal axes, i.e., H∥[0001] (c axis) and H∥[112[over ¯]0] (a axis), suggesting the presence of nodal quasiparticle excitations from heavy bands. At low temperatures, the polar-angle (θ) dependence of C exhibits a maximum along H∥[0001] with a twofold symmetric oscillation below 0.5 T, and an unusual shoulder or hump anomaly has been found around 30°-60° from the c axis in C(θ) at intermediate fields (1≲μ_{0}H≲2  T). These behaviors in UPd_{2}Al_{3} purely come from the superconducting nodal quasiparticle excitations, and can be successfully reproduced by theoretical calculations assuming the gap symmetry with a horizontal linear line node. We demonstrate the whole angle-resolved heat-capacity measurements done here as a novel spectroscopic method for nodal gap determination, which can be applied to other exotic superconductors.

  9. Precursor State to Unconventional Superconductivity in CeIrIn5.

    PubMed

    Nair, Sunil; Wirth, S; Nicklas, M; Sarrao, J L; Thompson, J D; Fisk, Z; Steglich, F

    2008-04-04

    We present Hall effect and magnetoresistance measurements in the heavy fermion superconductor CeIrIn(5). At low temperature, a Kondo coherent state is established. Deviations from Kohler's rule and a quadratic temperature dependence of the cotangent of the Hall angle are reminiscent of properties observed in the high-temperature superconducting cuprates. A striking observation pertains to the presence of a precursor state--characterized by a change in the Hall mobility--that precedes the superconductivity in this material, in similarity to the pseudogap in the cuprate superconductors.

  10. NMR evidence of anisotropic Kondo liquid behavior in CeIrIn5

    NASA Astrophysics Data System (ADS)

    Shockley, A. C.; Shirer, K. R.; Crocker, J.; Dioguardi, A. P.; Lin, C. H.; Nisson, D. M.; apRoberts-Warren, N.; Klavins, P.; Curro, N. J.

    2015-08-01

    We report detailed Knight-shift measurements of the two indium sites in the heavy-fermion compound CeIrIn5 as a function of temperature and field orientation. We find that the Knight-shift anomaly is orientation dependent, with a crossover temperature T* that varies by 50% as the field is rotated from (001) to (100). This result suggests that the hybridization between the Ce 4 f states and the itinerant conduction electrons is anisotropic, a result that reflects its collective origin, and may lead to anisotropic Kondo liquid behavior and unconventional superconductivity.

  11. Bold Diagrammatic Monte Carlo for Fermionic and Fermionized Systems

    NASA Astrophysics Data System (ADS)

    Svistunov, Boris

    2013-03-01

    In three different fermionic cases--repulsive Hubbard model, resonant fermions, and fermionized spins-1/2 (on triangular lattice)--we observe the phenomenon of sign blessing: Feynman diagrammatic series features finite convergence radius despite factorial growth of the number of diagrams with diagram order. Bold diagrammatic Monte Carlo technique allows us to sample millions of skeleton Feynman diagrams. With the universal fermionization trick we can fermionize essentially any (bosonic, spin, mixed, etc.) lattice system. The combination of fermionization and Bold diagrammatic Monte Carlo yields a universal first-principle approach to strongly correlated lattice systems, provided the sign blessing is a generic fermionic phenomenon. Supported by NSF and DARPA

  12. Bootstrapping 3D fermions

    DOE PAGES

    Iliesiu, Luca; Kos, Filip; Poland, David; ...

    2016-03-17

    We study the conformal bootstrap for a 4-point function of fermions <ψψψψ> in 3D. We first introduce an embedding formalism for 3D spinors and compute the conformal blocks appearing in fermion 4-point functions. Using these results, we find general bounds on the dimensions of operators appearing in the ψ × ψ OPE, and also on the central charge CT. We observe features in our bounds that coincide with scaling dimensions in the GrossNeveu models at large N. Finally, we also speculate that other features could coincide with a fermionic CFT containing no relevant scalar operators.

  13. Bootstrapping 3D fermions

    SciTech Connect

    Iliesiu, Luca; Kos, Filip; Poland, David; Pufu, Silviu S.; Simmons-Duffin, David; Yacoby, Ran

    2016-03-17

    We study the conformal bootstrap for a 4-point function of fermions <ψψψψ> in 3D. We first introduce an embedding formalism for 3D spinors and compute the conformal blocks appearing in fermion 4-point functions. Using these results, we find general bounds on the dimensions of operators appearing in the ψ × ψ OPE, and also on the central charge CT. We observe features in our bounds that coincide with scaling dimensions in the GrossNeveu models at large N. Finally, we also speculate that other features could coincide with a fermionic CFT containing no relevant scalar operators.

  14. Canonical gravity with fermions

    SciTech Connect

    Bojowald, Martin; Das, Rupam

    2008-09-15

    Canonical gravity in real Ashtekar-Barbero variables is generalized to allow for fermionic matter. The resulting torsion changes several expressions in Holst's original vacuum analysis, which are summarized here. This in turn requires adaptations to the known loop quantization of gravity coupled to fermions, which is discussed on the basis of the classical analysis. As a result, parity invariance is not manifestly realized in loop quantum gravity.

  15. Triplet fermions and Dirac fermions in borophene

    NASA Astrophysics Data System (ADS)

    Ezawa, Motohiko

    2017-07-01

    Borophene is a monolayer materials made of boron. A perfect planar boropehene called β12 borophene has Dirac cones and they are well reproduced by a tight-binding model according to recent experimental and first-principles calculation results. We explicitly derive a Dirac theory for β12 borophene. Dirac cones are gapless when the inversion symmetry exists, while they are gapped when it is broken. In addition, three-band touching points emerge together with pseudospin triplet fermions when all transfer energy is equal and all onsite energy is equal. The three-band touching is slightly resolved otherwise. We construct effective three-band theories for triplet fermions. We also study the edge states of borophene nanoribbons, which show various behaviors depending on the way of edge terminations.

  16. Superconductivity in the boson-fermion model with short range fermion repulsion

    NASA Astrophysics Data System (ADS)

    Kostyrko, Tomasz

    1998-03-01

    We consider influence of an on-site Coulomb repulsion U between fermions on superconducting properties of a two-component system of the wide band electrons hybridized with heavy boson-like local electron pairs^1,2. Within an RPA treatment valid for U< fermion bandwidth, we show that U almost completely suppresses superconductivity as long as a boson level stays above a Fermi level (BCS limit), reducing both Tc and a range of stability of an s-wave superconducting phase at T=0 K. In a Bose region, where the chemical potential remains pinned to the boson level, superconductivity is always stable at T=0 K and suppression of Tc is relatively small, especially for finite values of a boson mass. Above results are verified with the conclusions based on an effective t-J like hamiltonian derived by means of a canonical perturbation method from the boson-fermion model in a strong U limit. We show that the on-site boson-fermion hybridization is reduced by a factor of 2t/U (t - fermion hopping) and transforms into an intersite coupling supporting an extended s-wave superconducting order in this limit. [1em] 1. J. Ranninger and Robaszkiewicz, Physica B 135, 468 (1985). 2. R. Friedberg and T.D. Lee, Phys. Rev. B 40, 423 (1989).

  17. Heavy fermion spin liquid in herbertsmithite

    NASA Astrophysics Data System (ADS)

    Shaginyan, V. R.; Amusia, M. Ya.; Msezane, A. Z.; Popov, K. G.; Stephanovich, V. A.

    2015-09-01

    We analyze recent heat capacity measurements in herbertsmithite ZnCu3(OH)6Cl2 single crystal samples subjected to strong magnetic fields. We show that the temperature dependence of specific heat Cmag formed by quantum spin liquid at different magnetic fields B resembles the electronic heat capacity Cel of the HF metal YbRh2Si2. We demonstrate that the spinon effective mass Mmag* ∝Cmag / T exhibits a scaling behavior like that of Cel / T. We also show that the recent measurements of Cmag are compatible with those obtained on powder samples. These observations allow us to conclude that ZnCu3(OH)6Cl2 holds a stable strongly correlated quantum spin liquid, and a possible gap in the spectra of spinon excitations is absent even under the application of very high magnetic fields of 18 T.

  18. Scattering of fermions by gravitons

    NASA Astrophysics Data System (ADS)

    Ulhoa, S. C.; Santos, A. F.; Khanna, Faqir C.

    2017-04-01

    The interaction between gravitons and fermions is investigated in the teleparallel gravity. The scattering of fermions and gravitons in the weak field approximation is analyzed. The transition amplitudes of M\\varnothing ller, Compton and new gravitational scattering are calculated.

  19. Fermion Monte Carlo

    SciTech Connect

    Kalos, M. H.; Pederiva, F.

    1998-12-01

    We review the fundamental challenge of fermion Monte Carlo for continuous systems, the "sign problem". We seek that eigenfunction of the many-body Schriodinger equation that is antisymmetric under interchange of the coordinates of pairs of particles. We describe methods that depend upon the use of correlated dynamics for pairs of correlated walkers that carry opposite signs. There is an algorithmic symmetry between such walkers that must be broken to create a method that is both exact and as effective as for symmetric functions, In our new method, it is broken by using different "guiding" functions for walkers of opposite signs, and a geometric correlation between steps of their walks, With a specific process of cancellation of the walkers, overlaps with antisymmetric test functions are preserved. Finally, we describe the progress in treating free-fermion systems and a fermion fluid with 14 3He atoms.

  20. Bosonization of Weyl Fermions

    NASA Astrophysics Data System (ADS)

    Marino, Eduardo

    The electron, discovered by Thomson by the end of the nineteenth century, was the first experimentally observed particle. The Weyl fermion, though theoretically predicted since a long time, was observed in a condensed matter environment in an experiment reported only a few weeks ago. Is there any linking thread connecting the first and the last observed fermion (quasi)particles? The answer is positive. By generalizing the method known as bosonization, the first time in its full complete form, for a spacetime with 3+1 dimensions, we are able to show that both electrons and Weyl fermions can be expressed in terms of the same boson field, namely the Kalb-Ramond anti-symmetric tensor gauge field. The bosonized form of the Weyl chiral currents lead to the angle-dependent magneto-conductance behavior observed in these systems.

  1. Boson/Fermion Janus Particles

    NASA Astrophysics Data System (ADS)

    Tsekov, R.

    2017-04-01

    Thermodynamically, bosons and fermions differ by their statistics only. A general entropy functional is proposed by superposition of entropic terms, typical for different quantum gases. The statistical properties of the corresponding Janus particles are derived by variation of the weight of the boson/fermion fraction. It is shown that di-bosons and anti-fermions separate in gas and liquid phases, while three-phase equilibrium appears for poly-boson/fermion Janus particles.

  2. Bipartite Composite Fermion States

    NASA Astrophysics Data System (ADS)

    Sreejith, G. J.; Tőke, C.; Wójs, A.; Jain, J. K.

    2011-08-01

    We study a class of ansatz wave functions in which composite fermions form two correlated “partitions.” These “bipartite” composite fermion states are demonstrated to be very accurate for electrons in a strong magnetic field interacting via a short-range 3-body interaction potential over a broad range of filling factors. Furthermore, this approach gives accurate approximations for the exact Coulomb ground state at 2+3/5 and 2+4/7 and is thus a promising candidate for the observed fractional quantum Hall states at the hole conjugate fractions at 2+2/5 and 2+3/7.

  3. Bipartite composite fermion States.

    PubMed

    Sreejith, G J; Toke, C; Wójs, A; Jain, J K

    2011-08-19

    We study a class of ansatz wave functions in which composite fermions form two correlated "partitions." These "bipartite" composite fermion states are demonstrated to be very accurate for electrons in a strong magnetic field interacting via a short-range 3-body interaction potential over a broad range of filling factors. Furthermore, this approach gives accurate approximations for the exact Coulomb ground state at 2+3/5 and 2+4/7 and is thus a promising candidate for the observed fractional quantum Hall states at the hole conjugate fractions at 2+2/5 and 2+3/7.

  4. Radiative seesaw-type mechanism of fermion masses and non-trivial quark mixing

    NASA Astrophysics Data System (ADS)

    Arbeláez, Carolina; Hernández, A. E. Cárcamo; Kovalenko, Sergey; Schmidt, Ivan

    2017-06-01

    We propose a predictive inert two-Higgs doublet model, where the standard model (SM) symmetry is extended by S3⊗ Z2⊗ Z_{12} and the field content is enlarged by extra scalar fields, charged exotic fermions and two heavy right-handed Majorana neutrinos. The charged exotic fermions generate a non-trivial quark mixing and provide one-loop-level masses for the first- and second-generation charged fermions. The masses of the light active neutrinos are generated from a one-loop-level radiative seesaw mechanism. Our model successfully explains the observed SM fermion mass and mixing pattern.

  5. Fermionic T-duality in fermionic double space

    NASA Astrophysics Data System (ADS)

    Nikolić, B.; Sazdović, B.

    2017-04-01

    In this article we offer the interpretation of the fermionic T-duality of the type II superstring theory in double space. We generalize the idea of double space doubling the fermionic sector of the superspace. In such doubled space fermionic T-duality is represented as permutation of the fermionic coordinates θα and θbarα with the corresponding fermionic T-dual ones, ϑα and ϑbarα, respectively. Demanding that T-dual transformation law has the same form as initial one, we obtain the known form of the fermionic T-dual NS-R and R-R background fields. Fermionic T-dual NS-NS background fields are obtained under some assumptions. We conclude that only symmetric part of R-R field strength and symmetric part of its fermionic T-dual contribute to the fermionic T-duality transformation of dilaton field and analyze the dilaton field in fermionic double space. As a model we use the ghost free action of type II superstring in pure spinor formulation in approximation of constant background fields up to the quadratic terms.

  6. Fermion number anomaly with the fluffy mirror fermion

    NASA Astrophysics Data System (ADS)

    Okumura, Ken-ichi; Suzuki, Hiroshi

    2016-12-01

    Quite recently, Grabowska and Kaplan presented a 4-dimensional lattice formulation of chiral gauge theories based on the chiral overlap operator. We study this formulation from the perspective of the fermion number anomaly and possible associated phenomenology. A simple argument shows that the consistency of the formulation implies that the fermion with the opposite chirality to the physical one, the "fluffy mirror fermion" or "fluff", suffers from the fermion number anomaly in the same magnitude (with the opposite sign) as the physical fermion. This immediately shows that if at least one of the fluff quarks is massless, the formulation provides a simple viable solution to the strong CP problem. Also, if the fluff interacts with gravity essentially in the same way as the physical fermion, the formulation can realize the asymmetric dark matter scenario.

  7. Damping rates and mean free paths of soft fermion collective excitations in a hot fermion-gauge-scalar theory

    SciTech Connect

    Wang, S.-Y.; Boyanovsky, D.; Vega, H. J. de; Lee, D.-S.; Ng, Y. J.

    2000-03-15

    We study the transport coefficients, damping rates, and mean free paths of soft fermion collective excitations in a hot fermion-gauge-scalar plasma with the goal of understanding the main physical mechanisms that determine transport of chirality in scenarios of nonlocal electroweak baryogenesis. The focus is on identifying the different transport coefficients for the different branches of soft collective excitations of the fermion spectrum. These branches correspond to collective excitations with opposite ratios of chirality to helicity and different dispersion relations. By combining results from the hard thermal loop (HTL) resummation program with a novel mechanism of fermion damping through heavy scalar decay, we obtain a robust description of the different damping rates and mean free paths for the soft collective excitations to leading order in HTL and lowest order in the Yukawa coupling. The space-time evolution of wave packets of collective excitations unambiguously reveals the respective mean free paths. We find that whereas both the gauge and scalar contribution to the damping rates are different for the different branches, the difference of mean free paths for both branches is mainly determined by the decay of the heavy scalar into a hard fermion and a soft collective excitation. We argue that these mechanisms are robust and are therefore relevant for nonlocal scenarios of baryogenesis either in the standard model or extensions thereof. (c) 2000 The American Physical Society.

  8. Linear dependencies between composite fermion states

    NASA Astrophysics Data System (ADS)

    Meyer, M. L.; Liabøtrø, O.; Viefers, S.

    2016-09-01

    The formalism of composite fermions (CFs) has been one of the most prominent and successful approaches to describing the fractional quantum Hall effect, in terms of trial many-body wave functions. Testing the accuracy of the latter typically involves rather heavy numerical comparison to exact diagonalization results. Thus, optimizing computational efficiency has been an important technical issue in this field. One generic (and not yet fully understood) property of the CF approach is that it tends to overcount the number of linearly independent candidate states for fixed sets of quantum numbers. Technically speaking, CF Slater determinants that are orthogonal before projection to the lowest Landau level, may lead to wave functions that are identical, or possess linear dependencies, after projection. This leads to unnecessary computations, and has been pointed out in the literature both for fermionic and bosonic systems. We here present a systematic approach that enables us to reveal all linear dependencies between bosonic compact states in the lowest CF ‘cyclotron energy’ sub-band, and almost all dependencies in higher sub-bands, at the level of the CF Slater determinants, i.e. before projection, which implies a major computational simplification. Our approach is introduced for so-called simple states of two-species rotating bosons, and then generalized to generic compact bosonic states, both one- and two-species. Some perspectives also apply to fermionic systems. The identities and linear dependencies we find, are analytically exact for ‘brute force’ projection in the disk geometry.

  9. Leptogenesis from split fermions

    SciTech Connect

    Nagatani, Yukinori; Perez, Gilad

    2004-01-11

    We present a new type of leptogenesis mechanism based on a two-scalar split-fermions framework. At high temperatures the bulk scalar vacuum expectation values (VEVs) vanish and lepton number is strongly violated. Below some temperature, T{sub c}, the scalars develop extra dimension dependent VEVs. This transition is assumed to proceed via a first order phase transition. In the broken phase the fermions are localized and lepton number violation is negligible. The lepton-bulk scalar Yukawa couplings contain sizable CP phases which induce lepton production near the interface between the two phases. We provide a qualitative estimation of the resultant baryon asymmetry which agrees with current observation. The neutrino flavor parameters are accounted for by the above model with an additional approximate U(1) symmetry.

  10. Tripartite composite fermion states

    NASA Astrophysics Data System (ADS)

    Sreejith, G. J.; Wu, Ying-Hai; Wójs, A.; Jain, J. K.

    2013-06-01

    The Read-Rezayi wave function is one of the candidates for the fractional quantum Hall effect at filling fraction ν=2+⅗, and thereby also its hole conjugate at 2+⅖. We study a general class of tripartite composite fermion wave functions, which reduce to the Rezayi-Read ground state and quasiholes for appropriate quantum numbers, but also allow a construction of wave functions for quasiparticles and neutral excitations by analogy to the standard composite fermion theory. We present numerical evidence in finite systems that these trial wave functions capture well the low energy physics of a four-body model interaction. We also compare the tripartite composite fermion wave functions with the exact Coulomb eigenstates at 2+⅗, and find reasonably good agreement. The ground state as well as several excited states of the four-body interaction are seen to evolve adiabatically into the corresponding Coulomb states for N=15 particles. These results support the plausibility of the Read-Rezayi proposal for the 2+⅖ and 2+⅗ fractional quantum Hall effect. However, certain other proposals also remain viable, and further study of excitations and edge states will be necessary for a decisive establishment of the physical mechanism of these fractional quantum Hall states.

  11. Topology and Fermionic Condensate

    NASA Astrophysics Data System (ADS)

    Kulikov, I.; Pronin, P.

    The purpose of this paper is to investigate an influence of a space-time topology on the formation of fermionic condensate in the model with four-fermion interaction ()2. The value for the space-time with topology of R1 × R1 × S1 is found. Moreover a relation of the value of fermionic condensate to a periodic length is studied. In this connection the possibility of a relation of the topologic deposits to structure of hadrons is discussed.Translated AbstractTopologie und FermikondensatEs wird der Einfluß einer Raum-Zeittopologie auf die Bildung des Fermikondensats in einem Modell mit Vierfermionenwechselwirkung ()2 untersucht. Für eine Raum-Zeit mit der Topologie R1 × R2 × S1 werden die Parameter gegeben. Weiterhin wird die Relation der Größe des Fermikondensats zu einer periodischen Länge untersucht. In diesem Zusammenhang wird die Verbindung des topologischen Depots zur Struktur der Hadronen diskutiert.

  12. Hadron Properties with FLIC Fermions

    SciTech Connect

    James Zanotti; Wolodymyr Melnitchouk; Anthony Williams; J Zhang

    2003-07-01

    The Fat-Link Irrelevant Clover (FLIC) fermion action provides a new form of nonperturbative O(a)-improvement in lattice fermion actions offering near continuum results at finite lattice spacing. It provides computationally inexpensive access to the light quark mass regime of QCD where chiral nonanalytic behavior associated with Goldstone bosons is revealed. The motivation and formulation of FLIC fermions, its excellent scaling properties and its low-lying hadron mass phenomenology are presented.

  13. Fermion mass without symmetry breaking

    NASA Astrophysics Data System (ADS)

    Catterall, Simon

    2016-01-01

    We examine a model of reduced staggered fermions in three dimensions interacting through an SO (4) invariant four fermion interaction. The model is similar to that considered in a recent paper by Ayyer and Chandrasekharan [1]. We present theoretical arguments and numerical evidence which support the idea that the system develops a mass gap for sufficiently strong four fermi coupling without producing a symmetry breaking fermion bilinear condensate. Massless and massive phases appear to be separated by a continuous phase transition.

  14. Fermion mass without symmetry breaking

    DOE PAGES

    Catterall, Simon

    2016-01-20

    We examine a model of reduced staggered fermions in three dimensions interacting through an SO (4) invariant four fermion interaction. The model is similar to that considered in a recent paper by Ayyer and Chandrasekharan. We present theoretical arguments and numerical evidence which support the idea that the system develops a mass gap for sufficiently strong four fermi coupling without producing a symmetry breaking fermion bilinear condensate. As a result, massless and massive phases appear to be separated by a continuous phase transition.

  15. Cloaking two-dimensional fermions

    SciTech Connect

    Lin, De-Hone

    2011-09-15

    A cloaking theory for a two-dimensional spin-(1/2) fermion is proposed. It is shown that the spinor of the two-dimensional fermion can be cloaked perfectly through controlling the fermion's energy and mass in a specific manner moving in an effective vector potential inside a cloaking shell. Different from the cloaking of three-dimensional fermions, the scaling function that determines the invisible region is uniquely determined by a nonlinear equation. It is also shown that the efficiency of the cloaking shell is unaltered under the Aharonov-Bohm effect.

  16. Search for Majorana Fermions in S-Wave Fermionic Superfluids

    DTIC Science & Technology

    2016-04-01

    Atomic and molecular physics Objectives and research goals Majorana fermions were envisioned by E. Majorana in 1935 to describe neutrinos . The Majorana...were initially conceived to describe neutrinos in particle physics. Recently, Weyl fermions have been widely examined in a class of solid-state

  17. Multi-regulator functional renormalization group for many-fermion systems

    NASA Astrophysics Data System (ADS)

    Tanizaki, Yuya; Hatsuda, Tetsuo

    We propose a method of multi-regulator functional renormalization group (MR-FRG) which is a novel formulation of functional renormalization group with multiple infrared (IR) regulators. It is applied to a two-component fermionic system with an attractive contact interaction to study crossover phenomena between the Bardeen-Cooper-Schrieffer (BCS) phase and the Bose-Einstein condensation (BEC) phase. To control both the fermionic one-particle excitations and the bosonic collective excitations, IR regulators are introduced, one for the fermionic two-point function and another for the four-fermion vertex. It is shown that the Nozières-Schmitt-Rink (NSR) theory, which is successful to capture qualitative features of the BCS-BEC crossover, can be derived from MR-FRG. Some aspects of MR-FRG to go beyond the NSR theory are also discussed.

  18. Probing the fermionic Higgs portal at lepton colliders

    SciTech Connect

    Fedderke, Michael A.; Lin, Tongyan; Wang, Lian -Tao

    2016-04-26

    Here, we study the sensitivity of future electron-positron colliders to UV completions of the fermionic Higgs portal operator HHχ¯χ. Measurements of precision electroweak S and T parameters and the e+e → Zh cross-section at the CEPC, FCC-ee, and ILC are considered. The scalar completion of the fermionic Higgs portal is closely related to the scalar Higgs portal, and we summarize existing results. We devote the bulk of our analysis to a singlet-doublet fermion completion. Assuming the doublet is sufficiently heavy, we construct the effective field theory (EFT) at dimension-6 in order to compute contributions to the observables. We also provide full one-loop results for S and T in the general mass parameter space. In both completions, future precision measurements can probe the new states at the (multi-)TeV scale, beyond the direct reach of the LHC.

  19. Probing the fermionic Higgs portal at lepton colliders

    DOE PAGES

    Fedderke, Michael A.; Lin, Tongyan; Wang, Lian -Tao

    2016-04-26

    Here, we study the sensitivity of future electron-positron colliders to UV completions of the fermionic Higgs portal operator H†Hχ¯χ. Measurements of precision electroweak S and T parameters and the e+e– → Zh cross-section at the CEPC, FCC-ee, and ILC are considered. The scalar completion of the fermionic Higgs portal is closely related to the scalar Higgs portal, and we summarize existing results. We devote the bulk of our analysis to a singlet-doublet fermion completion. Assuming the doublet is sufficiently heavy, we construct the effective field theory (EFT) at dimension-6 in order to compute contributions to the observables. We also providemore » full one-loop results for S and T in the general mass parameter space. In both completions, future precision measurements can probe the new states at the (multi-)TeV scale, beyond the direct reach of the LHC.« less

  20. Majorana fermions in vortex lattices

    NASA Astrophysics Data System (ADS)

    Biswas, Rudro

    2013-03-01

    We consider Majorana fermions tunneling between vortices, within an array of such vortices in a 2D chiral p-wave superconductor. We calculate that the tunneling amplitude for Majorana fermions in a pair of vortices is proportional to the sine of half the difference between the global order parameter phases at the two vortices. Using this result we study tight-binding models of Majorana fermions in vortices arranged in a triangular or square lattice. In both cases we find that this phase-tunneling relationship leads to the creation of superlattices where the Majorana fermions form macroscopically degenerate `flat' bands at zero energy, in addition to other dispersive bands. This finding suggests that in vortex arrays tunneling processes do not change the energies of a finite fraction of Majorana fermions and hence brighten the prospects of topological quantum computing with a large number of Majorana states.

  1. Three-dimensional Majorana fermions in chiral superconductors.

    PubMed

    Kozii, Vladyslav; Venderbos, Jörn W F; Fu, Liang

    2016-12-01

    Using a systematic symmetry and topology analysis, we establish that three-dimensional chiral superconductors with strong spin-orbit coupling and odd-parity pairing generically host low-energy nodal quasiparticles that are spin-nondegenerate and realize Majorana fermions in three dimensions. By examining all types of chiral Cooper pairs with total angular momentum J formed by Bloch electrons with angular momentum j in crystals, we obtain a comprehensive classification of gapless Majorana quasiparticles in terms of energy-momentum relation and location on the Fermi surface. We show that the existence of bulk Majorana fermions in the vicinity of spin-selective point nodes is rooted in the nonunitary nature of chiral pairing in spin-orbit-coupled superconductors. We address experimental signatures of Majorana fermions and find that the nuclear magnetic resonance spin relaxation rate is significantly suppressed for nuclear spins polarized along the nodal direction as a consequence of the spin-selective Majorana nature of nodal quasiparticles. Furthermore, Majorana nodes in the bulk have nontrivial topology and imply the presence of Majorana bound states on the surface, which form arcs in momentum space. We conclude by proposing the heavy fermion superconductor PrOs4Sb12 and related materials as promising candidates for nonunitary chiral superconductors hosting three-dimensional Majorana fermions.

  2. Three-dimensional Majorana fermions in chiral superconductors

    PubMed Central

    Kozii, Vladyslav; Venderbos, Jörn W. F.; Fu, Liang

    2016-01-01

    Using a systematic symmetry and topology analysis, we establish that three-dimensional chiral superconductors with strong spin-orbit coupling and odd-parity pairing generically host low-energy nodal quasiparticles that are spin-nondegenerate and realize Majorana fermions in three dimensions. By examining all types of chiral Cooper pairs with total angular momentum J formed by Bloch electrons with angular momentum j in crystals, we obtain a comprehensive classification of gapless Majorana quasiparticles in terms of energy-momentum relation and location on the Fermi surface. We show that the existence of bulk Majorana fermions in the vicinity of spin-selective point nodes is rooted in the nonunitary nature of chiral pairing in spin-orbit–coupled superconductors. We address experimental signatures of Majorana fermions and find that the nuclear magnetic resonance spin relaxation rate is significantly suppressed for nuclear spins polarized along the nodal direction as a consequence of the spin-selective Majorana nature of nodal quasiparticles. Furthermore, Majorana nodes in the bulk have nontrivial topology and imply the presence of Majorana bound states on the surface, which form arcs in momentum space. We conclude by proposing the heavy fermion superconductor PrOs4Sb12 and related materials as promising candidates for nonunitary chiral superconductors hosting three-dimensional Majorana fermions. PMID:27957543

  3. projective variational study on low-temperature quantum magnetism in Na4Ir3O8

    NASA Astrophysics Data System (ADS)

    Shindou, Ryuichi

    2015-03-01

    Na4Ir3O8 is one of candidate materials of three-dimensional quantum spin liquid Mott isnulator, where Ir J=1/2 spin forms a hyperkagome lattice, a corner-sharing triangle network lattice with spin frustration. Due to lack of spatial inversion symmetries and heavy atom nature of Iridium, the system possesses larger anisotropic exchange interactions. In fact, preceding theories based on ab-initio band calculation show that Dzyaloshinskii-Moriya (DM) interaction is on order of 10 percent of isotropic exchange interaction, which could play vital role of highly competing grand state energetics in Na4Ir3O8. From transport experiments, the system is also known to be in weak Mott insulating regime, where charge fluctuation cause larger multiple-spin interactions. Employing variational analyses based on projective(fermionic) construction of many-body spin wavefunctions, we will reconsider possible quantum spin ground states in the hyperkagome antiferromagnetic Heisenberg model with anisotropic exchange and multiple-spin interactions of Na4Ir3O8. Starting from these states, we will discuss possible magnetic excitations and compare them with reported experiments.

  4. Hierarchy spectrum of SM fermions: from top quark to electron neutrino

    NASA Astrophysics Data System (ADS)

    Xue, She-Sheng

    2016-11-01

    In the SM gauge symmetries and fermion content of neutrinos, charged leptons and quarks, we study the effective four-fermion operators of Einstein-Cartan type and their contributions to the Schwinger-Dyson equations of fermion self-energy functions. The study is motivated by the speculation that these four-fermion operators are probably originated due to the quantum gravity, which provides the natural regularization for chiral-symmetric gauge field theories. In the chiral-gauge symmetry breaking phase, as to achieve the energetically favorable ground state, only the top-quark mass is generated via the spontaneous symmetry breaking, and other fermion masses are generated via the explicit symmetry breaking induced by the top-quark mass, four-fermion interactions and fermion-flavor mixing matrices. A phase transition from the symmetry breaking phase to the chiral-gauge symmetric phase at TeV scale occurs and the drastically fine-tuning problem can be resolved. In the infrared fixed-point domain of the four-fermion coupling for the SM at low energies, we qualitatively obtain the hierarchy patterns of the SM fermion Dirac masses, Yukawa couplings and family-flavor mixing matrices with three additional right-handed neutrinos ν R f . Large Majorana masses and lepton-number symmetry breaking are originated by the four-fermion interactions among ν R f and their left-handed conjugated fields ν R fc . Light masses of gauged Majorana neutrinos in the normal hierarchy (10-5 - 10-2 eV) are obtained consistently with neutrino oscillations. We present some discussions on the composite Higgs phenomenology and forward-backward asymmetry of toverline{t} -production, as well as remarks on the candidates of light and heavy dark matter particles (fermions, scalar and pseudoscalar bosons).

  5. Dirac Fermions in Borophene.

    PubMed

    Feng, Baojie; Sugino, Osamu; Liu, Ro-Ya; Zhang, Jin; Yukawa, Ryu; Kawamura, Mitsuaki; Iimori, Takushi; Kim, Howon; Hasegawa, Yukio; Li, Hui; Chen, Lan; Wu, Kehui; Kumigashira, Hiroshi; Komori, Fumio; Chiang, Tai-Chang; Meng, Sheng; Matsuda, Iwao

    2017-03-03

    Honeycomb structures of group IV elements can host massless Dirac fermions with nontrivial Berry phases. Their potential for electronic applications has attracted great interest and spurred a broad search for new Dirac materials especially in monolayer structures. We present a detailed investigation of the β_{12} sheet, which is a borophene structure that can form spontaneously on a Ag(111) surface. Our tight-binding analysis revealed that the lattice of the β_{12} sheet could be decomposed into two triangular sublattices in a way similar to that for a honeycomb lattice, thereby hosting Dirac cones. Furthermore, each Dirac cone could be split by introducing periodic perturbations representing overlayer-substrate interactions. These unusual electronic structures were confirmed by angle-resolved photoemission spectroscopy and validated by first-principles calculations. Our results suggest monolayer boron as a new platform for realizing novel high-speed low-dissipation devices.

  6. Dirac Fermions in Borophene

    NASA Astrophysics Data System (ADS)

    Feng, Baojie; Sugino, Osamu; Liu, Ro-Ya; Zhang, Jin; Yukawa, Ryu; Kawamura, Mitsuaki; Iimori, Takushi; Kim, Howon; Hasegawa, Yukio; Li, Hui; Chen, Lan; Wu, Kehui; Kumigashira, Hiroshi; Komori, Fumio; Chiang, Tai-Chang; Meng, Sheng; Matsuda, Iwao

    2017-03-01

    Honeycomb structures of group IV elements can host massless Dirac fermions with nontrivial Berry phases. Their potential for electronic applications has attracted great interest and spurred a broad search for new Dirac materials especially in monolayer structures. We present a detailed investigation of the β12 sheet, which is a borophene structure that can form spontaneously on a Ag(111) surface. Our tight-binding analysis revealed that the lattice of the β12 sheet could be decomposed into two triangular sublattices in a way similar to that for a honeycomb lattice, thereby hosting Dirac cones. Furthermore, each Dirac cone could be split by introducing periodic perturbations representing overlayer-substrate interactions. These unusual electronic structures were confirmed by angle-resolved photoemission spectroscopy and validated by first-principles calculations. Our results suggest monolayer boron as a new platform for realizing novel high-speed low-dissipation devices.

  7. Fermions in worldline holography

    NASA Astrophysics Data System (ADS)

    Dietrich, Dennis D.; Koenigstein, Adrian

    2017-09-01

    We analyze the worldline holographic framework for fermions. Worldline holography is based on the observation that in the worldline approach to quantum field theory, sources of a quantum field theory over Mink4 naturally form a field theory over AdS5 to all orders in the elementary fields and in the sources. Schwinger's proper time of the worldline formalism automatically appears with the physical four spacetime dimensions in an AdS5 geometry. The worldline holographic effective action in general and the proper-time profiles of the sources in particular solve a renormalization group equation. By taking into account sources up to spin one, we reconstruct seminal holographic models. Considering spin two confirms AdS5 as a consistent background.

  8. The comparison of two heavy fuel oils in composition and weathering pattern, based on IR, GC-FID and GC-MS analyses: application to the Prestige wreackage.

    PubMed

    Fernández-Varela, R; Andrade, J M; Muniategui, S; Prada, D; Ramírez-Villalobos, F

    2009-03-01

    This paper compares the weathering patterns of two similar fuel oils: a fuel oil spilled after a ship accident (Prestige-Nassau, off the Galician coast -NW Spain-) and a fuel designed to cope with the numerous quests for samples to carry out scientific studies (IFO). Comparative studies were made to evaluate the capability of common fingerprinting analytical techniques to differentiate the fuels, as well as their capabilities to monitor their weathering. The two products were spilled under controlled conditions during ca. four months to assess how they evolved on time. Mid-IR spectrometry and gas chromatography (flame ionization and mass spectrometry detectors) were used. IR indexes related to total aromaticity, type of substituents (branched or linear chains) and degree of aromatic substitution reflected well the differences between the fuels during weathering. Regarding the chromatographic measurements, the n-alkanes became highly reduced for both fuel oils and it was found that the PAHs of the synthetic fuel (IFO) were more resistant to weathering. Regarding biomarkers, the different profiles of the steranes, diasteranes and triaromatic steroids allowed for a simple differentiation amongst the two products. The %D2/P2 ratio differentiated both products whereas the %N3/P2 one ordered the samples according to the extent of their weathering.

  9. Fermion mass without symmetry breaking

    SciTech Connect

    Catterall, Simon

    2016-01-20

    We examine a model of reduced staggered fermions in three dimensions interacting through an SO (4) invariant four fermion interaction. The model is similar to that considered in a recent paper by Ayyer and Chandrasekharan. We present theoretical arguments and numerical evidence which support the idea that the system develops a mass gap for sufficiently strong four fermi coupling without producing a symmetry breaking fermion bilinear condensate. As a result, massless and massive phases appear to be separated by a continuous phase transition.

  10. Composite fermion-boson mapping for fermionic lattice models.

    PubMed

    Zhao, J; Jiménez-Hoyos, C A; Scuseria, G E; Huerga, D; Dukelsky, J; Rombouts, S M A; Ortiz, G

    2014-11-12

    We present a mapping of elementary fermion operators onto a quadratic form of composite fermionic and bosonic cluster operators. The mapping is an exact isomorphism as long as the physical constraint of one composite particle per cluster is satisfied. This condition is treated on average in a composite particle mean-field approach, which consists of an ansatz that decouples the composite fermionic and bosonic sectors. The theory is tested on the 1D and 2D Hubbard models. Using a Bogoliubov determinant for the composite fermions and either a coherent or Bogoliubov state for the bosons, we obtain a simple and accurate procedure for treating the Mott insulating phase of the Hubbard model with mean-field computational cost.

  11. Effective fermion kinematics from modified quantum gravity

    NASA Astrophysics Data System (ADS)

    Alexandre, J.; Leite, J.

    2016-10-01

    We consider a classical fermion and a classical scalar, propagating on two different kinds of four-dimensional diffeomorphism breaking gravity backgrounds, and we derive the one-loop effective dispersion relation for matter, after integrating out gravitons. One gravity model involves quadratic divergences at one-loop, as in Einstein gravity, and the other model is the z = 3 non-projectable Horava-Lifshitz gravity, which involves logarithmic divergences only. Although these two models behave differently in the ultraviolet, the IR phenomenology for matter fields is comparable: (i) for generic values for the parameters, both models identify 1010 GeV as the characteristic scale above which they are not consistent with current upper bounds on Lorentz symmetry violation; (ii) for both models, there is always a fine-tuning of parameters which allows the cancellation of the indicator for Lorentz symmetry violation.

  12. X-ray absorption studies of the local structure and f-level occupancy in CeIr(1-x)Rh(x)In(5)

    SciTech Connect

    Daniel, M.; Han, S.-W.; Booth, C.H.; Cornelius, A.L.; Pagliuso, P.G.; Sarrao, J.L.; Thompson, J.D.

    2004-04-15

    The CeIr{sub 1-x}Rh{sub x}In{sub 5} series exhibits a range of interesting phenomena, including heavy-fermion superconductivity, non-Fermi liquid behavior, and concomitant antiferromagnetism (AF) and superconductivity (SC). In the low-Rh concentration range (0.1 {ge} x {ge} 0.5), specific heat measurements show a broad anomaly, suggestive of gross phase separation. We have performed x-ray absorption experiments at the Ce L{sub III}, Ir L{sub III}, and Rh K-edges as a function of Rh concentration and temperature. X-ray absorption near-edge structure (XANES) measurements indicate that cerium is close to trivalent in this system, with no measurable change with temperature from 20-300 K, consistent with a heavy-fermion material. Extended x-ray absorption fine structure (EXAFS) measurements as a function of temperature from all measured edges indicate the local crystal structure of all samples is well ordered, with no gross phase separation observed, even for samples with x = 0.125 and x = 0.25. These results therefore suggest that the anomalous specific heat behavior in the 0.1 {ge} x {ge} 0.5 range have some other explanation, and some possibilities are discussed.

  13. Bipartite entanglement in fermion systems

    NASA Astrophysics Data System (ADS)

    Gigena, N.; Rossignoli, R.

    2017-06-01

    We discuss the relation between fermion entanglement and bipartite entanglement. We first show that an exact correspondence between them arises when the states are constrained to have a definite local number parity. Moreover, for arbitrary states in a four-dimensional single-particle Hilbert space, the fermion entanglement is shown to measure the entanglement between two distinguishable qubits defined by a suitable partition of this space. Such entanglement can be used as a resource for tasks like quantum teleportation. On the other hand, this fermionic entanglement provides a lower bound to the entanglement of an arbitrary bipartition, although in this case the local states involved will generally have different number parities. Finally, the fermionic implementation of the teleportation and superdense coding protocols based on qubits with odd and even number parity is discussed, together with the role of the previous types of entanglement.

  14. Spontaneous compactification and chiral fermions

    NASA Astrophysics Data System (ADS)

    Frampton, Paul H.; Yamamoto, Katsuji

    The question is addressed of which chiral fermions survive in spontaneously compactified solutions of the generalized Einstein-Yang-Mills field equations for higher even space-time dimensions. First, we study the allowed fermion representations of SU( N) which have no gauge or gravitational chiral anomalies in arbitrary even dimension and show how to find all such representations for the case of totally antisymmetric SU( N) tensors. Second, we look explicitly at monopole-induced spontaneous compactification in six dimensions; here, interesting chiral fermions in four dimensions do not occur easily but instead require highly artificial assignments of quantum numbers under the U(1) gauge group associated with the monopole. Finally, we consider instanton-induced spontaneous compactification in eight dimensions; for this case, we may readily obtain acceptable chiral fermions in four dimensions, including Georgi's three-family SU(11) model.

  15. Observing remnants by fermions' tunneling

    SciTech Connect

    Chen, D.Y.; Wu, H.W.; Yang, H. E-mail: iverwu@uestc.edu.cn

    2014-03-01

    The standard Hawking formula predicts the complete evaporation of black holes. In this paper, we introduce effects of quantum gravity into fermions' tunneling from Reissner-Nordstrom and Kerr black holes. The quantum gravity effects slow down the increase of Hawking temperatures. This property naturally leads to a residue mass in black hole evaporation. The corrected temperatures are affected by the quantum numbers of emitted fermions. Meanwhile, the temperature of the Kerr black hole is a function of θ due to the rotation.

  16. Fermions as generalized Ising models

    NASA Astrophysics Data System (ADS)

    Wetterich, C.

    2017-04-01

    We establish a general map between Grassmann functionals for fermions and probability or weight distributions for Ising spins. The equivalence between the two formulations is based on identical transfer matrices and expectation values of products of observables. The map preserves locality properties and can be realized for arbitrary dimensions. We present a simple example where a quantum field theory for free massless Dirac fermions in two-dimensional Minkowski space is represented by an asymmetric Ising model on a euclidean square lattice.

  17. Majorana fermions in a box

    NASA Astrophysics Data System (ADS)

    Al-Hashimi, M. H.; Shalaby, A. M.; Wiese, U.-J.

    2017-03-01

    Motivated by potential applications to ultracold matter, we perform a theoretical study of Majorana fermions confined to a finite volume, whose boundary conditions are characterized by self-adjoint extension parameters. While the boundary conditions for Dirac fermions in (1 +1 )-d are characterized by a 1-parameter family, λ =-λ*, of self-adjoint extensions, for Majorana fermions λ is restricted to ±i . Based on this result, we compute the frequency spectrum of Majorana fermions confined to a 1-d interval. The boundary conditions for Dirac fermions confined to a 3-d region of space are characterized by a 4-parameter family of self-adjoint extensions, which is reduced to two distinct 1-parameter families for Majorana fermions. We also consider the problems related to the quantum mechanical interpretation of the Majorana equation as a single-particle equation. Furthermore, the equation is related to a relativistic Schrödinger equation that does not suffer from these problems. Here we restrict ourselves to theoretical considerations without yet focusing on concrete cold matter applications.

  18. Charge carrier holes and Majorana fermions

    NASA Astrophysics Data System (ADS)

    Liang, Jingcheng; Lyanda-Geller, Yuli

    2017-05-01

    Understanding Luttinger holes in low dimensions is crucial for numerous spin-dependent phenomena and nanotechnology. In particular, hole quantum wires that are proximity coupled to a superconductor is a promising system for the observation of Majorana fermions. Earlier treatments of confined Luttinger holes ignored a mutual transformation of heavy and light holes at the heteroboundaries. We derive the effective hole Hamiltonian in the ground state. The mutual transformation of holes is crucial for Zeeman and spin-orbit coupling, and results in several spin-orbit terms linear in momentum in hole quantum wires. We discuss the criterion for realizing Majorana modes in charge carrier hole systems. GaAs or InSb hole wires shall exhibit stronger topological superconducting pairing, and provide additional opportunities for its control compared to InSb electron systems.

  19. Cu(Ir1 − xCrx)2S4: a model system for studying nanoscale phase coexistence at the metal-insulator transition

    PubMed Central

    Božin, E. S.; Knox, K. R.; Juhás, P.; Hor, Y. S.; Mitchell, J. F.; Billinge, S. J. L.

    2014-01-01

    Increasingly, nanoscale phase coexistence and hidden broken symmetry states are being found in the vicinity of metal-insulator transitions (MIT), for example, in high temperature superconductors, heavy fermion and colossal magnetoresistive materials, but their importance and possible role in the MIT and related emergent behaviors is not understood. Despite their ubiquity, they are hard to study because they produce weak diffuse signals in most measurements. Here we propose Cu(Ir1 − xCrx)2S4 as a model system, where robust local structural signals lead to key new insights. We demonstrate a hitherto unobserved coexistence of an Ir4+ charge-localized dimer phase and Cr-ferromagnetism. The resulting phase diagram that takes into account the short range dimer order is highly reminiscent of a generic MIT phase diagram similar to the cuprates. We suggest that the presence of quenched strain from dopant ions acts as an arbiter deciding between the competing ground states. PMID:24518384

  20. Fermions and gravitational gyrotropy

    NASA Astrophysics Data System (ADS)

    Helfer, Adam D.

    2016-12-01

    In conventional general relativity without torsion, high-frequency gravitational waves couple to the chiral number density of spin one-half quanta: the polarization of the waves is rotated by 2 π N5ℓPl2, where N5 is the chiral column density and ℓPl is the Planck length. This means that if a primordial distribution of gravitational waves with E-E or B-B correlations passed through a chiral density of fermions in the very early Universe, an E-B correlation will be generated. This in turn will give rise to E-B and T-B correlations in the cosmic microwave background (CMB). Less obviously but more primitively, the condition Albrecht called "cosmic coherence" would be violated, changing the restrictions on the class of admissible cosmological gravitational waves. This altered class of waves would, generally speaking, probe earlier physics than do the conventional waves; their effects on the CMB would be most pronounced for low (≲100 ) multipoles. Rough estimates indicate that if the tensor-to-scalar ratio is less than about 10-2, it will be hard to constrain a spatially homogeneous primordial N5 by present data.

  1. Charged Lifshitz black hole and probed Lorentz-violation fermions from holography

    NASA Astrophysics Data System (ADS)

    Luo, Cheng-Jian; Kuang, Xiao-Mei; Shu, Fu-Wen

    2017-06-01

    We analytically obtain a new charged Lifshitz solution by adding a non-relativistic Maxwell field in Hořava-Lifshitz gravity. The black hole exhibits an anisotropic scaling between space and time (Lifshitz scaling) in the UV limit, while in the IR limit, the Lorentz invariance is approximately recovered. We introduce the probed Lorentz-violation fermions into the background and holographically investigate the spectral properties of the dual fermionic operator. The Lorentz-violation of the fermions will enhance the peak and correspond larger fermi momentum, which compensates the non-relativistic bulk effect of the dynamical exponent (z). For a fixed z, when the Lorentz-violation of fermions increases to a critical value, the behavior of the low energy excitation goes from a non-Fermi liquid type to a Fermi liquid type, which implies a kind of phase transition.

  2. Toward the classification of the realistic free fermionic models

    SciTech Connect

    Faraggi, A.E.

    1997-08-01

    The realistic free fermionic models have had remarkable success in providing plausible explanations for various properties of the Standard Model which include the natural appearance of three generations, the explanation of the heavy top quark mass and the qualitative structure of the fermion mass spectrum in general, the stability of the proton and more. These intriguing achievements makes evident the need to understand the general space of these models. While the number of possibilities is large, general patterns can be extracted. In this paper the author presents a detailed discussion on the construction of the realistic free fermionic models with the aim of providing some insight into the basic structures and building blocks that enter the construction. The role of free phases in the determination of the phenomenology of the models is discussed in detail. The author discusses the connection between the free phases and mirror symmetry in (2,2) models and the corresponding symmetries in the case of (2,0) models. The importance of the free phases in determining the effective low energy phenomenology is illustrated in several examples. The classification of the models in terms of boundary condition selection rules, real world-sheet fermion pairings, exotic matter states and the hidden sector is discussed.

  3. Studying fermionic ghost imaging with independent photons

    NASA Astrophysics Data System (ADS)

    Liu, Jianbin; Zhou, Yu; Zheng, Huaibin; Chen, Hui; Li, Fu-li; Xu, Zhuo

    2016-12-01

    Ghost imaging with thermal fermions is calculated based on two-particle interference in Feynman's path integral theory. It is found that ghost imaging with thermal fermions can be simulated by ghost imaging with thermal bosons and classical particles. Photons in pseudothermal light are employed to experimentally study fermionic ghost imaging. Ghost imaging with thermal bosons and fermions is discussed based on the point-to-point (spot) correlation between the object and image planes. The employed method offers an efficient guidance for future ghost imaging with real thermal fermions, which may also be generalized to study other second-order interference phenomena with fermions.

  4. Electronic structure of Ce2RhIn8: A two-dimensional heavy-fermion system studied by angle-resolved photoemission spectroscopy

    SciTech Connect

    Jiang, Rui; Mou, Daixing; Liu, Chang; Zhao, Xin; Yao, Yongxin; Ryu, Hyejin; Petrovic, C.; Ho, Kai -Ming; Kaminski, Adam

    2015-04-01

    In this study, we use angle-resolved photoemission spectroscopy (ARPES) to study the two-dimensional (2D) heavy-fermion superconductor, Ce2 RhIn8. The Fermi surface is rather complicated and consists of several hole and electron pockets with one of the sheets displaying strong nesting properties with a q vector of (0.32, 0.32) π/a. We do not observe kz dispersion of the Fermi sheets, which is consistent with the expected 2D character of the electronic structure. Comparison of the ARPES data to band-structure calculations suggests that a localized picture of the f electrons works best. While there is some agreement in the overall band dispersion and location of the Fermi sheets, the model does not reproduce all observed bands and is not completely accurate for those it does. Our data paves the way for improving the band-structure calculations and the general understanding of the transport and thermodynamical properties of this material.

  5. Majorana Fermions in Vortex Lattices

    NASA Astrophysics Data System (ADS)

    Biswas, Rudro R.

    2013-09-01

    We consider Majorana fermions tunneling among an array of vortices in a 2D chiral p-wave superconductor or equivalent material. The amplitude for Majorana fermions to tunnel between a pair of vortices is found to necessarily depend on the background superconducting phase profile; it is found to be proportional to the sine of half the difference between the phases at the two vortices. Using this result we study tight-binding models of Majorana fermions in vortices arranged in triangular or square lattices. In both cases we find that the aforementioned phase-tunneling relationship leads to the creation of superlattices where the Majorana fermions form macroscopically degenerate localizable flat bands at zero energy, in addition to other dispersive bands. This finding suggests that tunneling processes in these vortex arrays do not change the energies of a finite fraction of Majorana fermions, contrary to previous expectation. The presence of flat Majorana bands, and hence less-than-expected decoherence in these vortex arrays, bodes well for the prospects of topological quantum computation with large numbers of Majorana states.

  6. Majorana fermions in vortex lattices.

    PubMed

    Biswas, Rudro R

    2013-09-27

    We consider Majorana fermions tunneling among an array of vortices in a 2D chiral p-wave superconductor or equivalent material. The amplitude for Majorana fermions to tunnel between a pair of vortices is found to necessarily depend on the background superconducting phase profile; it is found to be proportional to the sine of half the difference between the phases at the two vortices. Using this result we study tight-binding models of Majorana fermions in vortices arranged in triangular or square lattices. In both cases we find that the aforementioned phase-tunneling relationship leads to the creation of superlattices where the Majorana fermions form macroscopically degenerate localizable flat bands at zero energy, in addition to other dispersive bands. This finding suggests that tunneling processes in these vortex arrays do not change the energies of a finite fraction of Majorana fermions, contrary to previous expectation. The presence of flat Majorana bands, and hence less-than-expected decoherence in these vortex arrays, bodes well for the prospects of topological quantum computation with large numbers of Majorana states.

  7. Dual-fermion approach to interacting disordered fermion systems

    NASA Astrophysics Data System (ADS)

    Yang, S.-X.; Haase, P.; Terletska, H.; Meng, Z. Y.; Pruschke, T.; Moreno, J.; Jarrell, M.

    2014-05-01

    We generalize the recently introduced dual-fermion (DF) formalism for disordered fermion systems by including the effect of interactions. For an interacting disordered system the contributions to the full vertex function have to be separated into crossing-asymmetric and crossing-symmetric scattering processes, and addressed differently when constructing the DF diagrams. By applying our approach to the Anderson-Falicov-Kimball model and systematically restoring the nonlocal correlations in the DF lattice calculation, we show a significant improvement over the dynamical mean-field theory and the coherent potential approximation for both one-particle and two-particle quantities.

  8. Dual-fermion approach to interacting disordered fermion systems

    NASA Astrophysics Data System (ADS)

    Yang, Shuxiang; Haase, Patrick; Terletska, Hanna; Meng, Zi Yang; Pruschke, Thomas; Moreno, Juana; Jarrell, Mark

    2014-03-01

    We generalize the recently introduced dual fermion (DF) formalism for disordered fermion systems by including the effect of interactions. For an interacting disordered system the contributions to the full vertex function have to be separated into elastic and inelastic scattering processes, and addressed differently when constructing the DF diagrams. By applying our approach to the Anderson-Falicov-Kimball model and systematically restoring the nonlocal correlations in the DF lattice calculation, we show a significant improvement over the Dynamical Mean-Field Theory and the Coherent Potential Approximation for both one-particle and two-particle quantities.

  9. Local spin operators for fermion simulations

    NASA Astrophysics Data System (ADS)

    Whitfield, James D.; Havlíček, Vojtěch; Troyer, Matthias

    2016-09-01

    Digital quantum simulation of fermionic systems is important in the context of chemistry and physics. Simulating fermionic models on general purpose quantum computers requires imposing a fermionic algebra on qubits. The previously studied Jordan-Wigner and Bravyi-Kitaev transformations are two techniques for accomplishing this task. Here, we reexamine an auxiliary fermion construction which maps fermionic operators to local operators on qubits. The local simulation is performed by relaxing the requirement that the number of qubits should match the number of single-particle states. Instead, auxiliary sites are introduced to enable nonconsecutive fermionic couplings to be simulated with constant low-rank tensor products on qubits. The additional number of auxiliary qubits required per fermionic degree of freedom depends only on the degree of connectivity of the Hamiltonian. We connect the auxiliary fermion construction to topological models and give examples of the construction.

  10. Fermion localization on thick branes

    SciTech Connect

    Melfo, Alejandra; Pantoja, Nelson; Tempo, Jose David

    2006-02-15

    We consider chiral fermion confinement in scalar thick branes, which are known to localize gravity, coupled through a Yukawa term. The conditions for the confinement and their behavior in the thin-wall limit are found for various different BPS branes, including double walls and branes interpolating between different AdS{sub 5} spacetimes. We show that only one massless chiral mode is localized in all these walls, whenever the wall thickness is keep finite. We also show that, independently of wall's thickness, chiral fermionic modes cannot be localized in dS{sub 4} walls embedded in a M{sub 5} spacetime. Finally, massive fermions in double wall spacetimes are also investigated. We find that, besides the massless chiral mode localization, these double walls support quasilocalized massive modes of both chiralities.

  11. Mass-imbalanced fermionic mixture in a harmonic trap

    NASA Astrophysics Data System (ADS)

    Bazak, B.

    2017-08-01

    The mass-imbalanced fermionic mixture is studied, where N ≤5 identical fermions interact resonantly with an impurity, a distinguishable atom. The shell structure is explored, and the physics of a dynamic light-impurity is shown to be different from that of the static heavy-impurity case. The energies in a harmonic trap at unitarity are calculated and extrapolated to the zero-range limit. In doing so, the scale factor of the ground state, as well as of a few excited states, is calculated. In the 2 ≤N ≤4 systems, pure (N +1 ) Efimov states exist for large enough mass ratio. However, no sign for a six-body Efimov state in the (5 +1 ) system is found in the mass ratio explored, M /m ≤12 .

  12. Fast evaluation and locality of overlap fermions

    NASA Astrophysics Data System (ADS)

    Bietenholz, W.; Hip, I.; Schilling, K.

    2002-03-01

    In order to construct improved overlap fermions, we start from a short ranged approximate Ginsparg-Wilson fermion and insert it into the overlap formula. We show that its polynomial evaluation is accelerated considerably compared to the standard Neuberger fermion. In addition the degree of locality is strongly improved.

  13. Fast evaluation and locality of overlap fermions

    NASA Astrophysics Data System (ADS)

    Bietenholz, W.; Hip, I.; Schilling, K.

    In order to construct improved overlap fermions, we start from a short ranged approximate Ginsparg-Wilson fermion and insert it into the overlap formula. We show that its polynomial evaluation is accelerated considerably compared to the standard Neuberger fermion. In addition the degree of locality is strongly improved.

  14. Gravitational contribution to fermion masses

    NASA Astrophysics Data System (ADS)

    Tiemblo, A.; Tresguerres, R.

    2005-08-01

    In the context of a non-linear gauge theory of the Poincaré group, we show that covariant derivatives of Dirac fields include a coupling to the translational connections, manifesting itself in the matter action as a universal background mass contribution to fermions.

  15. Nonlinear fermions and coherent states

    NASA Astrophysics Data System (ADS)

    Trifonov, D. A.

    2012-06-01

    Nonlinear fermions of degree n (n-fermions) are introduced as particles with creation and annihilation operators obeying the simple nonlinear anticommutation relation AA† + A†nAn = 1. The (n + 1)th-order nilpotency of these operators follows from the existence of unique A-vacuum. Supposing appropriate (n + 1)th-order nilpotent para-Grassmann variables and integration rules the sets of n-fermion number states, ‘right’ and ‘left’ ladder operator coherent states (CS) and displacement-operator-like CS are constructed. The (n + 1) × (n + 1) matrix realization of the related para-Grassmann algebra is provided. General (n + 1)th-order nilpotent ladder operators of finite-dimensional systems are expressed as polynomials in terms of n-fermion operators. Overcomplete sets of (normalized) ‘right’ and ‘left’ eigenstates of such general ladder operators are constructed and their properties are briefly discussed. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Coherent states: mathematical and physical aspects’.

  16. Wilson fermions at finite temperature

    SciTech Connect

    Creutz, M.

    1996-09-17

    The author conjectures on the phase structure expected for lattice gauge theory with two flavors of Wilson fermions, concentrating on large values of the hopping parameter. Numerous phases are expected, including the conventional confinement and deconfinement phases, as well as an Aoki phase with spontaneous breaking of flavor and parity and a large hopping phase corresponding to negative quark masses.

  17. Constructing entanglement measures for fermions

    NASA Astrophysics Data System (ADS)

    Johansson, Markus; Raissi, Zahra

    2016-10-01

    In this paper we describe a method for finding polynomial invariants under stochastic local operations and classical communication (SLOCC) for a system of delocalized fermions shared between different parties, with global particle-number conservation as the only constraint. These invariants can be used to construct entanglement measures for different types of entanglement in such a system. It is shown that the invariants, and the measures constructed from them, take a nonzero value only if the state of the system allows for the observation of Bell-nonlocal correlations. Invariants of this kind are constructed for systems of two and three spin-1/2 fermions and examples of maximally entangled states are given that illustrate the different types of entanglement distinguished by the invariants. A general condition for the existence of SLOCC invariants and their associated measures is given as a relation between the number of fermions, their spin, and the number of spatial modes of the system. In addition, the effect of further constraints on the system, including the localization of a subset of the fermions, is discussed. Finally, a hybrid Ising-Hubbard Hamiltonian is constructed for which the ground state of a three-site chain exhibits a high degree of entanglement at the transition between a regime dominated by on-site interaction and a regime dominated by Ising interaction. This entanglement is well described by a measure constructed by the introduced method.

  18. Chronometric cosmology and fundamental fermions

    PubMed Central

    Segal, I. E.

    1982-01-01

    It is proposed that the fundamental fermions of nature are modeled by fields on the chronometric cosmos that are not precisely spinors but become such only in the nonchronometric limit. The imbedding of the scale-extended Poincaré group in the linearizer of the Minkowskian conformal group defines such fields, by induction. PMID:16593266

  19. Fermion fractionalization to Majorana fermions in a dimerized Kitaev superconductor

    NASA Astrophysics Data System (ADS)

    Wakatsuki, Ryohei; Ezawa, Motohiko; Tanaka, Yukio; Nagaosa, Naoto

    2014-07-01

    We study theoretically a one-dimensional dimerized Kitaev superconductor model which belongs to BDI class with time-reversal, particle-hole, and chiral symmetries. There are two sources of the particle-hole symmetry, i.e., the sublattice symmetry and superconductivity. Accordingly, we define two types of topological numbers with respect to the chiral indices of normal and Majorana fermions, which offers an ideal laboratory to examine the interference between the two different physics within the same symmetry class. Phase diagram, zero-energy bound states, and conductance at normal metal/superconductor junction of this model are unveiled from this viewpoint. Especially, the electron fractionalization to the Majorana fermions showing the splitting of the local density of states is realized at the soliton of the dimerization in this model.

  20. Fermion Fractionalization to Majorana Fermions in Dimerized Kitaev Superconductor

    NASA Astrophysics Data System (ADS)

    Wakatsuki, Ryohei; Ezawa, Motohiko; Tanaka, Yukio; Nagaosa, Naoto

    2015-03-01

    We study theoretically a one-dimensional dimerized Kitaev superconductor model which belongs to BDI class with time-reversal, particle-hole, and chiral symmetries. There are two sources of the particle-hole symmetry, i.e., the sublattice symmetry and superconductivity. Accordingly, we define two types of topological numbers with respect to the chiral indices of normal and Majorana fermions, which offers an ideal laboratory to examine the interference between the two different physics within the same symmetry class. Phase diagram, zero-energy bound states, and conductance at normal metal/superconductor junction of this model are unveiled from this viewpoint. Especially, the electron fractionalization to the Majorana fermions showing the splitting of the local density of states is realized at the soliton of the dimerization in this model.

  1. Effective field theory for dilute fermions with pairing

    SciTech Connect

    Furnstahl, R.J. Hammer, H.-W. Puglia, S.J.

    2007-11-15

    Effective field theory (EFT) methods for a uniform system of fermions with short-range, natural interactions are extended to include pairing correlations, as part of a program to develop a systematic Kohn-Sham density functional theory (DFT) for medium and heavy nuclei. An effective action formalism for local composite operators leads to a free-energy functional that includes pairing by applying an inversion method order by order in the EFT expansion. A consistent renormalization scheme is demonstrated for the uniform system through next-to-leading order, which includes induced-interaction corrections to pairing.

  2. Light scattering of degenerate fermions

    NASA Astrophysics Data System (ADS)

    Aubin, S.; Leblanc, L. J.; Myrskog, S.; Extavour, M. H. T.; McKay, D.; Stummer, A.; Thywissen, J. H.

    2006-05-01

    We report on progress in measuring the suppression of resonant light scattering in a gas of degenerate fermions. A gas of trapped degenerate fermions is expected to exhibit narrower optical linewidths and longer excited state lifetimes than single atoms when the Fermi energy is larger than the photon recoil energy [1-3]. In this case, the number of available states into which a scattered atom can recoil is significantly reduced due to the filling of the Fermi sea. We produce a degenerate gas of 4x10^4 ultra-cold fermionic ^40K atoms by sympathetic cooling with bosonic ^87Rb in a micro-magnetic chip trap. The atoms can then be loaded into a tight dipole trap just above the surface of the chip and probed with a near resonance laser pulse. [1] Th. Busch, J. R. Anglin, J. I. Cirac, and P. Zoller, Europhys. Lett. 44, 1 (1998). [2] B. DeMarco and D. S. Jin, Phys. Rev. A 58, R4267 (1998). [3] J. Javanainen and J. Ruostekosky, Phys. Rev. A 52, 3033 (1995). Work supported by NSERC, CFI, OIT, Research Corporation, and PRO.

  3. Superdeformations and fermion dynamical symmetries

    SciTech Connect

    Wu, Cheng-Li . Dept. of Physics and Atmospheric Science Tennessee Univ., Knoxville, TN . Dept. of Physics and Astronomy Joint Inst. for Heavy Ion Research, Oak Ridge, TN )

    1990-01-01

    In this talk, I will present a link between nuclear collective motions and their underlying fermion dynamical symmetries. In particular, I will focus on the microscopic understanding of deformations. It is shown that the SU{sub 3} of the one major shell fermion dynamical symmetry model (FDSM) is responsible for the physics of low and high spins in normal deformation. For the recently observed phenomena of superdeformation, the physics of the problem dictates a generalization to a supershell structure (SFDSM), which also has an SU{sub 3} fermion dynamical symmetry. Many recently discovered feature of superdeformation are found to be inherent in such an SU{sub 3} symmetry. In both cases the dynamical Pauli effect plays a vital role. A particularly noteworthy discovery from this model is that the superdeformed ground band is not the usual unaligned band but the D-pair aligned (DPA) band, which sharply crosses the excited bands. The existence of such DPA band is a key point to understand many properties of superdeformation. Our studies also poses new experimental challenge. This is particularly interesting since there are now plans to build new and exciting {gamma}-ray detecting systems, like the GAMMASPHERE, which could provide answers to some of these challenges. 34 refs., 11 figs., 5 tabs.

  4. Quantum Algorithms for Fermionic Simulations

    NASA Astrophysics Data System (ADS)

    Ortiz, Gerardo

    2001-06-01

    The probabilistic simulation of quantum systems in classical computers is known to be limited by the so-called sign or phase problem, a problem believed to be of exponential complexity. This ``disease" manifests itself by the exponentially hard task of estimating the expectation value of an observable with a given error. Therefore, probabilistic simulations on a classical computer do not seem to qualify as a practical computational scheme for general quantum many-body problems. The limiting factors, for whatever reasons, are negative or complex-valued probabilities whether the simulations are done in real or imaginary time. In 1981 Richard Feynman raised some provocative questions in connection to the ``exact imitation'' of such systems using a special device named a ``quantum computer.'' Feynman hesitated about the possibility of imitating fermion systems using such a device. Here we address some of his concerns and, in particular, investigate the simulation of fermionic systems. We show how quantum algorithms avoid the sign problem by reducing the complexity from exponential to polynomial. Our demonstration is based upon the use of isomorphisms of *-algebras (spin-particle transformations) which connect different models of quantum computation. In particular, we present fermionic models (the fabled ``Grassmann Chip''); but, of course, these models are not the only ones since our spin-particle connections allow us to introduce more ``esoteric'' models of computation. We present specific quantum algorithms that illustrate the main points of our algebraic approach.

  5. FCNC decays of standard model fermions into a dark photon

    NASA Astrophysics Data System (ADS)

    Gabrielli, Emidio; Mele, Barbara; Raidal, Martti; Venturini, Elena

    2016-12-01

    We analyze a new class of FCNC processes, the f →f'γ ¯ decays of a fermion f into a lighter (same-charge) fermion f' plus a massless neutral vector boson, a dark photon γ ¯. A massless dark photon does not interact at tree level with observable fields, and the f →f'γ ¯ decay presents a characteristic signature where the final fermion f' is balanced by a massless invisible system. Models recently proposed to explain the exponential spread in the standard-model Yukawa couplings can indeed foresee an extra unbroken dark U (1 ) gauge group, and the possibility to couple on-shell dark photons to standard-model fermions via one-loop magnetic-dipole kind of FCNC interactions. The latter are suppressed by the characteristic scale related to the mass of heavy messengers, connecting the standard model particles to the dark sector. We compute the corresponding decay rates for the top, bottom, and charm decays (t →c γ ¯ , u γ ¯ , b →s γ ¯ , d γ ¯ , and c →u γ ¯), and for the charged-lepton decays (τ →μ γ ¯ , e γ ¯ , and μ →e γ ¯) in terms of model parameters. We find that large branching ratios for both quark and lepton decays are allowed in case the messenger masses are in the discovery range of the LHC. Implications of these new decay channels at present and future collider experiments are briefly discussed.

  6. Local Hamiltonian Monte Carlo study of the massive schwinger model, the decoupling of heavy flavours

    NASA Astrophysics Data System (ADS)

    Ranft, J.

    1983-12-01

    The massive Schwinger model with two flavours is studied using the local hamiltonian lattice Monte Carlo method. Chiral symmetry breaking is studied using the fermion condensate as order parameter. For a small ratio of the two fermion masses, degeneracy of the two flavours is found. For a large ratio of the masses, the heavy flavour decouples and the light fermion behaves like in the one flavour Schwinger model. On leave from Sektion Physik, Karl-Marx-Universität, Leipzig, GDR.

  7. Aharonov-Bohm radiation of fermions

    SciTech Connect

    Chu Yizen; Mathur, Harsh; Vachaspati, Tanmay

    2010-09-15

    We analyze Aharonov-Bohm radiation of charged fermions from oscillating solenoids and cosmic strings. We find that the angular pattern of the radiation has features that differ significantly from that for bosons. For example, fermionic radiation in the lowest harmonic is approximately isotropically distributed around an oscillating solenoid, whereas for bosons the radiation is dipolar. We also investigate the spin polarization of the emitted fermion-antifermion pair. Fermionic radiation from kinks and cusps on cosmic strings is shown to depend linearly on the ultraviolet cutoff, suggesting strong emission at an energy scale comparable to the string energy scale.

  8. Light quark simulations with FLIC fermions

    SciTech Connect

    J.M. Zanotti; D.B. Leinweber; W. Melnitchouk; A.G. Williams; J.B. Zhang

    2002-06-01

    Hadron masses are calculated in quenched lattice QCD in order to probe the scaling behavior of a novel fat-link clover fermion action in which only the irrelevant operators of the fermion action are constructed using APE-smeared links. Light quark masses corresponding to an m{sub pi}/m{sub p} ratio of 0.35 are considered to assess the exceptional configuration problem of clover-fermion actions. This Fat-Link Irrelevant Clover (FLIC) fermion action provides scaling which is superior to mean-field improvement and offers advantages over nonperturbative improvement, including reduced exceptional configurations.

  9. Multipartite concurrence for identical-fermion systems

    NASA Astrophysics Data System (ADS)

    Majtey, A. P.; Bouvrie, P. A.; Valdés-Hernández, A.; Plastino, A. R.

    2016-03-01

    We study the problem of detecting multipartite entanglement among indistinguishable fermionic particles. A multipartite concurrence for pure states of N identical fermions, each one having a d -dimensional single-particle Hilbert space, is introduced. Such an entanglement measure, in particular, is optimized for maximally entangled states of three identical fermions that play a role analogous to the usual (qubit) Greenberger-Horne-Zeilinger state. In addition, it is shown that the fermionic multipartite concurrence can be expressed as the mean value of an observable, provided two copies of the composite state are available.

  10. Spin Tqfts and Fermionic Phases of Matter

    NASA Astrophysics Data System (ADS)

    Gaiotto, Davide; Kapustin, Anton

    We study lattice constructions of gapped fermionic phases of matter. We show that the construction of fermionic Symmetry Protected Topological orders by Gu and Wen has a hidden dependence on a discrete spin structure on the Euclidean space-time. The spin structure is needed to resolve ambiguities which are otherwise present. An identical ambiguity is shown to arise in the fermionic analog of the string-net construction of 2D topological orders. We argue that the need for a spin structure is a general feature of lattice models with local fermionic degrees of freedom and is a lattice analog of the spinstatistics relation.

  11. IR Windstreaks

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Windstreaks are features caused by the interaction of wind and topographic landforms. The raised rims and bowls of impact craters causes a complex interaction such that the wind vortex in the lee of the crater can both scour away the surface dust and deposit it back in the center of the lee. If you look closely, you will see evidence of this in a darker 'rim' enclosing a brighter interior.

    This infrared image shows windstreaks in the region between Gordii Dorsum and Amazonis Mensa.

    Image information: IR instrument. Latitude -15.8, Longitude 215 East (145 West). 97 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  12. IR Windstreaks

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Windstreaks are features caused by the interaction of wind and topographic landforms. The raised rims and bowls of impact craters causes a complex interaction such that the wind vortex in the lee of the crater can both scour away the surface dust and deposit it back in the center of the lee. If you look closely, you will see evidence of this in a darker 'rim' enclosing a brighter interior.

    This infrared image shows windstreaks in the region between Gordii Dorsum and Amazonis Mensa.

    Image information: IR instrument. Latitude -15.8, Longitude 215 East (145 West). 97 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  13. Is the Composite Fermion a Dirac Particle?

    NASA Astrophysics Data System (ADS)

    Son, Dam Thanh

    2015-07-01

    We propose a particle-hole symmetric theory of the Fermi-liquid ground state of a half-filled Landau level. This theory should be applicable for a Dirac fermion in the magnetic field at charge neutrality, as well as for the ν =1/2 quantum Hall ground state of nonrelativistic fermions in the limit of negligible inter-Landau-level mixing. We argue that when particle-hole symmetry is exact, the composite fermion is a massless Dirac fermion, characterized by a Berry phase of π around the Fermi circle. We write down a tentative effective field theory of such a fermion and discuss the discrete symmetries, in particular, C P . The Dirac composite fermions interact through a gauge, but non-Chern-Simons, interaction. The particle-hole conjugate pair of Jain-sequence states at filling factors n /(2 n +1 ) and (n +1 )/(2 n +1 ) , which in the conventional composite fermion picture corresponds to integer quantum Hall states with different filling factors, n and n +1 , is now mapped to the same half-integer filling factor n +1/2 of the Dirac composite fermion. The Pfaffian and anti-Pfaffian states are interpreted as d -wave Bardeen-Cooper-Schrieffer paired states of the Dirac fermion with orbital angular momentum of opposite signs, while s -wave pairing would give rise to a particle-hole symmetric non-Abelian gapped phase. When particle-hole symmetry is not exact, the Dirac fermion has a C P -breaking mass. The conventional fermionic Chern-Simons theory is shown to emerge in the nonrelativistic limit of the massive theory.

  14. STOUT SMEARING FOR TWISTED FERMIONS.

    SciTech Connect

    SCHOLZ,W.; JANSEN, K.; McNEILE, C.; MONTVAY, I.; RICHARDS, C.; URBACH, C.; WENGER, U.

    2007-07-30

    The effect of Stout smearing is investigated in numerical simulations with twisted mass Wilson quarks. The phase transition near zero quark mass is studied on 12{sup 3} x 24, 16{sup 3} x 32 and 24{sup 3} x 48 lattices at lattice spacings a {approx_equal} 0.1-0.125 fm. The phase structure of Wilson fermions with twisted mass ({mu}) has been investigated in [1,2]. As it is explained there, the observed first order phase transition limits the minimal pion mass which can be reached in simulations at a given lattice spacing: m{sub k}{sup min} {approx_equal} {theta}(a). The phase structure is schematically depicted in the left panel of Fig. I . The phase transition can be observed in simulations with twisted mass fermions, for instance, as a ''jump'' or even metastabilities in the average plaquette value as a function of the hopping parameter ({kappa}). One possibility to weaken the phase transition and therefore allow for lighter pion masses at a given lattice spacing is to use an improved gauge action like the DBW2, Iwasaki, or tree-level Symanzik (tlSym) improved gauge action instead of the simple Wilson gauge action. This has been successfully demonstrated in [3,4,5]. Here we report on our attempts to use a smeared gauge field in the fermion lattice Dirac operator to further reduce the strength of the phase transition. This is relevant in simulations with N{sub f} = 2 + 1 + 1 (u,d,s,c) quark flavors [6] where the first order phase transition becomes stronger compared to N{sub f} = 2 simulations. The main impact of the above mentioned improved gauge actions on the gauge fields occurring in simulations is to suppress short range fluctuations (''dislocations'') and the associated ''exceptionally small'' eigenvalues of the fermion matrix. The same effect is expected from smearing the gauge field links in the fermion action. The cumulated effect of the improved gauge action and smeared links should allow for a smaller pion mass at a given lattice spacing and volume. Our

  15. Fermion dipole moment and holography

    NASA Astrophysics Data System (ADS)

    Kulaxizi, Manuela; Rahman, Rakibur

    2015-12-01

    In the background of a charged AdS black hole, we consider a Dirac particle endowed with an arbitrary magnetic dipole moment. For non-zero charge and dipole coupling of the bulk fermion, we find that the dual boundary theory can be plagued with superluminal modes. Requiring consistency of the dual CFT amounts to constraining the strength of the dipole coupling by an upper bound. We briefly discuss the implications of our results for the physics of holographic non-Fermi liquids.

  16. Dipole oscillations in fermionic mixtures

    SciTech Connect

    Chiacchiera, S.; Macri, T.; Trombettoni, A.

    2010-03-15

    We study dipole oscillations in a general fermionic mixture. Starting from the Boltzmann equation, we classify the different solutions in the parameter space through the number of real eigenvalues of the small oscillations matrix. We discuss how this number can be computed using the Sturm algorithm and its relation with the properties of the Laplace transform of the experimental quantities. After considering two components in harmonic potentials having different trapping frequencies, we study dipole oscillations in three-component mixtures. Explicit computations are done for realistic experimental setups using the classical Boltzmann equation without intraspecies interactions. A brief discussion of the application of this classification to general collective oscillations is also presented.

  17. Coherent states in the fermionic Fock space

    NASA Astrophysics Data System (ADS)

    Oeckl, Robert

    2015-01-01

    We construct the coherent states in the sense of Gilmore and Perelomov for the fermionic Fock space. Our treatment is from the outset adapted to the infinite-dimensional case. The fermionic Fock space becomes in this way a reproducing kernel Hilbert space of continuous holomorphic functions.

  18. Superalgebra and fermion-boson symmetry

    PubMed Central

    Miyazawa, Hironari

    2010-01-01

    Fermions and bosons are quite different kinds of particles, but it is possible to unify them in a supermultiplet, by introducing a new mathematical scheme called superalgebra. In this article we discuss the development of the concept of symmetry, starting from the rotational symmetry and finally arriving at this fermion-boson (FB) symmetry. PMID:20228617

  19. Quantum electrodynamics with complex fermion mass

    SciTech Connect

    McKellar, B.J.H. . School of Physics); Wu, D.D. . School of Physics Academia Sinica, Beijing, BJ . Inst. of High Energy Physics Superconducting Super Collider Lab., Dallas, TX )

    1991-08-01

    The quantum electrodynamics (QED) with a complex fermion mass -- that is, a fermion mass with a chiral phase -- is restudied, together with its chirally rotated version. We show how fake electric dipole moment can be obtained and how to avoid it. 10 refs.

  20. Mass-induced transition in fermion number

    SciTech Connect

    Aragao de Carvalho, C.; Pureza, J. M.

    1989-05-15

    We show that if we increase the mass of fermions in interaction with a topological (kink) scalar background in 1+1 dimensions, the fractional fermion number of the system will eventually vanish. The transition is sharp and corresponds to the disappearance of localized states from the spectrum of a Dirac operator which is exactly solvable. Possible applications to different physical systems are discussed.

  1. Tunable Dirac Fermion Dynamics in Topological Insulators

    NASA Astrophysics Data System (ADS)

    Chen, Chaoyu; Xie, Zhuojin; Feng, Ya; Yi, Hemian; Liang, Aiji; He, Shaolong; Mou, Daixiang; He, Junfeng; Peng, Yingying; Liu, Xu; Liu, Yan; Zhao, Lin; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Yu, Li; Wang, Xiaoyang; Peng, Qinjun; Wang, Zhimin; Zhang, Shenjin; Yang, Feng; Chen, Chuangtian; Xu, Zuyan; Zhou, X. J.

    2013-08-01

    Three-dimensional topological insulators are characterized by insulating bulk state and metallic surface state involving relativistic Dirac fermions which are responsible for exotic quantum phenomena and potential applications in spintronics and quantum computations. It is essential to understand how the Dirac fermions interact with other electrons, phonons and disorders. Here we report super-high resolution angle-resolved photoemission studies on the Dirac fermion dynamics in the prototypical Bi2(Te,Se)3 topological insulators. We have directly revealed signatures of the electron-phonon coupling and found that the electron-disorder interaction dominates the scattering process. The Dirac fermion dynamics in Bi2(Te3-xSex) topological insulators can be tuned by varying the composition, x, or by controlling the charge carriers. Our findings provide crucial information in understanding and engineering the electron dynamics of the Dirac fermions for fundamental studies and potential applications.

  2. Causal fermions in discrete space-time

    NASA Astrophysics Data System (ADS)

    Farrelly, Terence C.; Short, Anthony J.

    2014-01-01

    In this paper, we consider fermionic systems in discrete space-time evolving with a strict notion of causality, meaning they evolve unitarily and with a bounded propagation speed. First, we show that the evolution of these systems has a natural decomposition into a product of local unitaries, which also holds if we include bosons. Next, we show that causal evolution of fermions in discrete space-time can also be viewed as the causal evolution of a lattice of qubits, meaning these systems can be viewed as quantum cellular automata. Following this, we discuss some examples of causal fermionic models in discrete space-time that become interesting physical systems in the continuum limit: Dirac fermions in one and three spatial dimensions, Dirac fields, and briefly the Thirring model. Finally, we show that the dynamics of causal fermions in discrete space-time can be efficiently simulated on a quantum computer.

  3. Tunable Dirac Fermion Dynamics in Topological Insulators

    PubMed Central

    Chen, Chaoyu; Xie, Zhuojin; Feng, Ya; Yi, Hemian; Liang, Aiji; He, Shaolong; Mou, Daixiang; He, Junfeng; Peng, Yingying; Liu, Xu; Liu, Yan; Zhao, Lin; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Yu, Li; Wang, Xiaoyang; Peng, Qinjun; Wang, Zhimin; Zhang, Shenjin; Yang, Feng; Chen, Chuangtian; Xu, Zuyan; Zhou, X. J.

    2013-01-01

    Three-dimensional topological insulators are characterized by insulating bulk state and metallic surface state involving relativistic Dirac fermions which are responsible for exotic quantum phenomena and potential applications in spintronics and quantum computations. It is essential to understand how the Dirac fermions interact with other electrons, phonons and disorders. Here we report super-high resolution angle-resolved photoemission studies on the Dirac fermion dynamics in the prototypical Bi2(Te,Se)3 topological insulators. We have directly revealed signatures of the electron-phonon coupling and found that the electron-disorder interaction dominates the scattering process. The Dirac fermion dynamics in Bi2(Te3−xSex) topological insulators can be tuned by varying the composition, x, or by controlling the charge carriers. Our findings provide crucial information in understanding and engineering the electron dynamics of the Dirac fermions for fundamental studies and potential applications. PMID:23934507

  4. Tunable Dirac fermion dynamics in topological insulators.

    PubMed

    Chen, Chaoyu; Xie, Zhuojin; Feng, Ya; Yi, Hemian; Liang, Aiji; He, Shaolong; Mou, Daixiang; He, Junfeng; Peng, Yingying; Liu, Xu; Liu, Yan; Zhao, Lin; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Yu, Li; Wang, Xiaoyang; Peng, Qinjun; Wang, Zhimin; Zhang, Shenjin; Yang, Feng; Chen, Chuangtian; Xu, Zuyan; Zhou, X J

    2013-01-01

    Three-dimensional topological insulators are characterized by insulating bulk state and metallic surface state involving relativistic Dirac fermions which are responsible for exotic quantum phenomena and potential applications in spintronics and quantum computations. It is essential to understand how the Dirac fermions interact with other electrons, phonons and disorders. Here we report super-high resolution angle-resolved photoemission studies on the Dirac fermion dynamics in the prototypical Bi2(Te,Se)3 topological insulators. We have directly revealed signatures of the electron-phonon coupling and found that the electron-disorder interaction dominates the scattering process. The Dirac fermion dynamics in Bi2(Te3-xSex) topological insulators can be tuned by varying the composition, x, or by controlling the charge carriers. Our findings provide crucial information in understanding and engineering the electron dynamics of the Dirac fermions for fundamental studies and potential applications.

  5. Optical spectra of the heavy fermion uniaxial ferromagnet UGe2

    NASA Astrophysics Data System (ADS)

    Guritanu, Violeta; Armitage, Peter; Tediosi, Riccardo; Saxena, Siddharth; Huxley, Andrew; van der Marel, Dirk

    2008-03-01

    We report on a detailed optical study of UGe2 single crystalline material using infrared reflectivity and spectroscopic ellipsometry. The optical conductivity suggests the presence of a low frequency interband transition ( 300 cm-1) and a narrow free-carrier response with strong frequency dependence of the scattering rate and effective mass. We observe sharp changes in the low frequency mass and scattering rate below the upper ferromagnetic transition TC1. They recover their unrenormalized value above TC1 and for φ> 250 cm-1. In contrast no sign of an anomaly is seen at TC2 ˜ 30 K, which is the lower transition of unknown nature. These observations are consistent with the weak anomaly observed at TC2 in transport and thermodynamic experiments.

  6. Surface resistance of the heavy-fermion superconductor UPt3

    NASA Astrophysics Data System (ADS)

    Grimes, C. C.; Adams, G.; Bucher, E.

    1991-09-01

    The surface resistance R of two UPt3 single crystals has been measured using an apparatus in which the direction of the rf or microwave current can be varied continuously relative to the crystal axes. In an a-axis single crystal at 0.38 K, R is found to be lower for current in the basal plane than for current along the c axis, while R is independent of current direction in a c-axis crystal. This suggests that the superconducting-energy-gap function is anisotropic with, on average, a larger gap in basal-plane directions than in the c-axis direction. R at 0.38 K is found to increase anomalously rapidly with increasing frequency to nearly the normal-state value at frequencies that are only a few percent of kTc.

  7. Fermion hierarchy from sfermion anarchy

    DOE PAGES

    Altmannshofer, Wolfgang; Frugiuele, Claudia; Harnik, Roni

    2014-12-31

    We present a framework to generate the hierarchical flavor structure of Standard Model quarks and leptons from loops of superpartners. The simplest model consists of the minimal supersymmetric standard model with tree level Yukawa couplings for the third generation only and anarchic squark and slepton mass matrices. Agreement with constraints from low energy flavor observables, in particular Kaon mixing, is obtained for supersymmetric particles with masses at the PeV scale or above. In our framework both the second and the first generation fermion masses are generated at 1-loop. Despite this, a novel mechanism generates a hierarchy among the first andmore » second generations without imposing a symmetry or small parameters. A second-to-first generation mass ratio of order 100 is typical. The minimal supersymmetric standard model thus includes all the necessary ingredients to realize a fermion spectrum that is qualitatively similar to observation, with hierarchical masses and mixing. The minimal framework produces only a few quantitative discrepancies with observation, most notably the muon mass is too low. Furthermore, we discuss simple modifications which resolve this and also investigate the compatibility of our model with gauge and Yukawa coupling Unification.« less

  8. Fermion hierarchy from sfermion anarchy

    SciTech Connect

    Altmannshofer, Wolfgang; Frugiuele, Claudia; Harnik, Roni

    2014-12-31

    We present a framework to generate the hierarchical flavor structure of Standard Model quarks and leptons from loops of superpartners. The simplest model consists of the minimal supersymmetric standard model with tree level Yukawa couplings for the third generation only and anarchic squark and slepton mass matrices. Agreement with constraints from low energy flavor observables, in particular Kaon mixing, is obtained for supersymmetric particles with masses at the PeV scale or above. In our framework both the second and the first generation fermion masses are generated at 1-loop. Despite this, a novel mechanism generates a hierarchy among the first and second generations without imposing a symmetry or small parameters. A second-to-first generation mass ratio of order 100 is typical. The minimal supersymmetric standard model thus includes all the necessary ingredients to realize a fermion spectrum that is qualitatively similar to observation, with hierarchical masses and mixing. The minimal framework produces only a few quantitative discrepancies with observation, most notably the muon mass is too low. Furthermore, we discuss simple modifications which resolve this and also investigate the compatibility of our model with gauge and Yukawa coupling Unification.

  9. Bosonization of free Weyl fermions

    NASA Astrophysics Data System (ADS)

    Marino, E. C.

    2017-03-01

    We generalize the method of bosonization, in its complete form, to a spacetime with 3  +  1 dimensions, and apply it to free Weyl fermion fields, which thereby, can be expressed in terms of a boson field, namely the Kalb-Ramond anti-symmetric tensor gauge field. The result may have interesting consequences both in condensed matter and in particle physics. In the former, the bosonized form of the Weyl chiral currents provides a simple explanation for the angle-dependent magneto-conductance recently observed in materials known as Weyl semimetals. In the latter, conversely, since electrons can be thought of as a combination of left and right Weyl fermions, our result suggests the possibility of a unified description of the elementary particles, which undergo the fundamental interactions, with the mediators of such interactions, namely, the gauge fields. This would fulfill the pioneering attempt of Skyrme, to unify the particles with their interaction mediators (Skyrme 1962 Nucl. Phys. 31 556).

  10. Cosmology of fermionic dark matter

    SciTech Connect

    Boeckel, Tillmann; Schaffner-Bielich, Juergen

    2007-11-15

    We explore a model for a fermionic dark matter particle family which decouples from the rest of the particles when at least all standard model particles are in equilibrium. We calculate the allowed ranges for mass and chemical potential to be compatible with big bang nucleosynthesis (BBN) calculations and WMAP data for a flat universe with dark energy ({omega}{sub {lambda}}{sup 0}=0.72, {omega}{sub M}{sup 0}=0.27, h=0.7). Futhermore we estimate the free streaming length for fermions and antifermions to allow comparison to large scale structure data (LSS). We find that for dark matter decoupling when all standard model particles are present even the least restrictive combined BBN calculation and WMAP results allow us to constrain the initial dark matter chemical potential to a highest value of 6.3 times the dark matter temperature. In this case, the resulting mass range is at most 1.8 eV{<=}m{<=}53 eV, where the upper bound scales linearly with g{sub eff}{sup s}(T{sub Dec}). From LSS we find that, similar to ordinary warm dark matter models, the particle mass has to be larger than {approx}500 eV [meaning g{sub eff}{sup s}(T{sub Dec})>10{sup 3}] to be compatible with observations of the Ly {alpha} forest at high redshift, but still the dark matter chemical potential over temperature ratio can exceed unity.

  11. Thermalization of Fermionic Quantum Walkers

    NASA Astrophysics Data System (ADS)

    Hamza, Eman; Joye, Alain

    2017-03-01

    We consider the discrete time dynamics of an ensemble of fermionic quantum walkers moving on a finite discrete sample, interacting with a reservoir of infinitely many quantum particles on the one dimensional lattice. The reservoir is given by a fermionic quasifree state, with free discrete dynamics given by the shift, whereas the free dynamics of the non-interacting quantum walkers in the sample is defined by means of a unitary matrix. The reservoir and the sample exchange particles at specific sites by a unitary coupling and we study the discrete dynamics of the coupled system defined by the iteration of the free discrete dynamics acting on the unitary coupling, in a variety of situations. In particular, in absence of correlation within the particles of the reservoir and under natural assumptions on the sample's dynamics, we prove that the one- and two-body reduced density matrices of the sample admit large times limits characterized by the state of the reservoir which are independent of the free dynamics of the quantum walkers and of the coupling strength. Moreover, the corresponding asymptotic density profile in the sample is flat and the correlations of number operators have no structure, a manifestation of thermalization.

  12. Fermion condensation and gapped domain walls in topological orders

    NASA Astrophysics Data System (ADS)

    Wan, Yidun; Wang, Chenjie

    2017-03-01

    We study fermion condensation in bosonic topological orders in two spatial dimensions. Fermion condensation may be realized as gapped domain walls between bosonic and fermionic topological orders, which may be thought of as real-space phase transitions from bosonic to fermionic topological orders. This picture generalizes the previous idea of understanding boson condensation as gapped domain walls between bosonic topological orders. While simple-current fermion condensation was considered before, we systematically study general fermion condensation and show that it obeys a Hierarchy Principle: a general fermion condensation can always be decomposed into a boson condensation followed by a minimal fermion condensation. The latter involves only a single self-fermion that is its own anti-particle and that has unit quantum dimension. We develop the rules of minimal fermion condensation, which together with the known rules of boson condensation, provides a full set of rules for general fermion condensation.

  13. Dual fermion approach for disordered interacting fermion systems

    NASA Astrophysics Data System (ADS)

    Yang, Shuxiang; Haase, Patrick; Terletska, Hanna; Meng, Ziyang; Moreno, Juana; Jarrell, Mark; Pruschke, Thomas

    2013-03-01

    Understanding the combined effect of electron-electron interaction and disorder is one of the crucial questions in condensed matter physics. There is an obvious need of theoretical tools which allow to treat both these effects on equal footing. To study the intricate interplay of these effects, we generalize our recently proposed dual fermion approach to include both electron-electron interaction and disorder. Since the constraint imposed on the dual-space Feynman diagrams in the disordered case does not apply to those generated due to interactions, it is essential to treat elastic scattering processes due to the disorder separately from the inelastic scattering processes due to the pure interaction and mixed contributions. I will discuss the resulting diagrammatic formalism and an algorithm for its implementation. The possible applications for the Anderson Falicov-Kimball and the Anderson-Hubbard models are also discussed.

  14. Semiclassical approach to dynamics of interacting fermions

    NASA Astrophysics Data System (ADS)

    Davidson, Shainen M.; Sels, Dries; Polkovnikov, Anatoli

    2017-09-01

    Understanding the behaviour of interacting fermions is of fundamental interest in many fields ranging from condensed matter to high energy physics. Developing numerically efficient and accurate simulation methods is an indispensable part of this. Already in equilibrium, fermions are notoriously hard to handle due to the sign problem. Out of equilibrium, an important outstanding problem is the efficient numerical simulation of the dynamics of these systems. In this work we develop a new semiclassical phase-space approach (a.k.a. the truncated Wigner approximation) for simulating the dynamics of interacting fermions in arbitrary dimensions. As fermions are essentially non-classical objects, a phase-space is constructed out of all fermionic bilinears. Classical phase-space is thus comprised of highly non-local (hidden) variables representing these bilinears, and the cost of the method is that it scales quadratic rather than linear with system size. We demonstrate the strength of the method by comparing the results to the exact quantum dynamics of fermion expansion in the Hubbard model and quantum thermalization in the Sachdev-Ye-Kitaev (SYK) model for small systems, where the semiclassics nearly perfectly reproduces correct results. We furthermore analyse fermion expansion in a larger, intractable by exact methods, 2D Hubbard model, which is directly relevant to recent cold atom experiments.

  15. New fermions in the bulk

    NASA Astrophysics Data System (ADS)

    de Brito, K. P. S.; da Rocha, Roldão

    2016-10-01

    The spinor fields on 5-dimensional Lorentzian manifolds are classified according to the geometric Fierz identities, which involve their bilinear covariants. Based upon this classification, which generalises the celebrated 4-dimensional Lounesto classification of spinor fields, new non-trivial classes of 5-dimensional spinor fields are hence found, with important potential applications regarding bulk fermions and their subsequent localisation on brane-worlds. In addition, quaternionic bilinear covariants are used to derive the quaternionic spin density through the truncated exterior bundle. In order to accomplish the realisation of these new spinors, a Killing vector field is constructed on the horizon of a 5-dimensional Kerr black hole. This Killing vector field is shown to reach the time-like Killing vector field at spatial infinity through a current 1-form density, constructed with the new derived spinor fields. The current density is, moreover, expressed as the fünfbein component, assuming a condensed form.

  16. Noncommutativity Parameter and Composite Fermions

    NASA Astrophysics Data System (ADS)

    Jellal, Ahmed

    We determine some particular values of the noncommutativity parameter θ and show that the Murthy Shankar approach is in fact a particular case of a more general one. Indeed, using the fractional quantum Hall effect (FQHE) experimental data, we give a measurement of θ. This measurement can be obtained by considering some values of the filling factor ν and other ingredients, magnetic field B and electron density ρ. Moreover, it is found that θ can be quantized either fractionally or integrally in terms of the magnetic length l0 and the quantization is exactly what Murthy and Shankar formulated recently for the FQHE. On the other hand, we show that the mapping of the FQHE in terms of the composite fermion basis has a noncommutative geometry nature and therefore there is a more general way than the Murthy Shankar method to do this mapping.

  17. An Exploratory Study of BK from NF = 2 Dynamical Clover-Improved Wilson Fermions

    NASA Astrophysics Data System (ADS)

    Flynn, J. M.; Mescia, F.; Tariq, A. S. B.

    2005-04-01

    We report calculations of BK using two flavours of dynamical clover-improved Wilson lattice fermions and look for dependence on the dynamical quark mass at fixed lattice spacing. We see some evidence for dynamical quark effects. In particular BK decreases as the sea quark masses are reduced towards the up/down quark mass. Our meson masses are quite heavy and a firm prediction of the BK value is a task for future simulations.

  18. BEC-polaron gas in a boson-fermion mixture: A many-body extension of Lee-Low-Pines theory

    NASA Astrophysics Data System (ADS)

    Nakano, Eiji; Yabu, Hiroyuki

    2016-05-01

    We investigate the ground state properties of the gaseous mixture of a single species of bosons and fermions at zero temperature, where bosons are major in population over fermions, and form the Bose-Einstein condensate (BEC). The boson-boson and boson-fermion interactions are assumed to be weakly repulsive and attractive, respectively, while the fermion-fermion interaction is absent due to the Pauli exclusion for the low energy s -wave scattering. We treat fermions as a gas of polarons dressed with Bogoliubov phonons, which is an elementary excitation of the BEC, and evaluate the ground state properties with the method developed by Lemmens, Devreese, and Brosens (LDB) originally for the electron polaron gas, and also with a general extension of the Lee-Low-Pines theory for many-body systems (eLLP), which incorporates the phonon drag effects as in the original LLP theory. The formulation of eLLP is developed and discussed in the present paper. The binding (interaction) energy of the polaron gas is calculated in these methods and shown to be finite (negative) for the dilute gas of heavy fermions with attractive boson-fermion interactions, though the suppression by the many-body effects exists.

  19. Discovery of Novel Dirac and Weyl Fermion Materials

    NASA Astrophysics Data System (ADS)

    Alidoust, Nasser

    In this dissertation, we present the experimental discovery of a new topological phase of matter, the Weyl semimetal state, in the monoarsenides TaAs and NbAs. Furthermore, we study various material systems with strong electron interactions, and provide compelling evidence for the existence of robust surface states in samarium hexaboride SmB6, as well as identify a Z2 topological insulator state with intriguing Dirac fermions in the low-carrier strongly-correlated cerium monopnictides CeBi and CeSb. We also investigate the honeycomb iridate Na2IrO3 and uncover linearly dispersing metallic states on its surface. Finally, we image the spin-orbit split valence band and the deposited quantum well states of the monolayer and bulk transition metal dichalcogenides MoS2 and MoSe2. The measurements presented in this dissertation constitute the first realization of emergent Weyl fermions in nature, introduce various directions for future discoveries of topological phases in strongly-correlated materials, and shed light on the spin-orbit physics of two-dimensional atomic crystals. These findings expand the field of topological phases of matter to gapless semimetallic and strongly-correlated materials, and offer great promises for further technological applications of topological materials in diverse platforms such as fault-tolerant qubits and low-power electronic and spintronic devices.

  20. Flavor symmetries and fermion masses

    SciTech Connect

    Rasin, Andrija

    1994-04-01

    We introduce several ways in which approximate flavor symmetries act on fermions and which are consistent with observed fermion masses and mixings. Flavor changing interactions mediated by new scalars appear as a consequence of approximate flavor symmetries. We discuss the experimental limits on masses of the new scalars, and show that the masses can easily be of the order of weak scale. Some implications for neutrino physics are also discussed. Such flavor changing interactions would easily erase any primordial baryon asymmetry. We show that this situation can be saved by simply adding a new charged particle with its own asymmetry. The neutrality of the Universe, together with sphaleron processes, then ensures a survival of baryon asymmetry. Several topics on flavor structure of the supersymmetric grand unified theories are discussed. First, we show that the successful predictions for the Kobayashi-Maskawa mixing matrix elements, Vub/Vcb = √mu/mc and Vtd/Vts = √md/ms, are a consequence of a large class of models, rather than specific properties of a few models. Second, we discuss how the recent observation of the decay β → sγ constrains the parameter space when the ratio of the vacuum expectation values of the two Higgs doublets, tanβ, is large. Finally, we discuss the flavor structure of proton decay. We observe a surprising enhancement of the branching ratio for the muon mode in SO(10) models compared to the same mode in the SU(5) model.

  1. Instantons and Massless Fermions in Two Dimensions

    DOE R&D Accomplishments Database

    Callan, C. G. Jr.; Dashen, R.; Gross, D. J.

    1977-05-01

    The role of instantons in the breakdown of chiral U(N) symmetry is studied in a two dimensional model. Chiral U(1) is always destroyed by the axial vector anomaly. For N = 2 chiral SU(N) is also spontaneously broken yielding massive fermions and three (decoupled) Goldstone bosons. For N greater than or equal to 3 the fermions remain massless. Realistic four dimensional theories are believed to behave in a similar way but the critical N above which the fermions cease to be massive is not known in four dimensions.

  2. Entanglement in fermion systems and quantum metrology

    NASA Astrophysics Data System (ADS)

    Benatti, F.; Floreanini, R.; Marzolino, U.

    2014-03-01

    Entanglement in fermion many-body systems is studied using a generalized definition of separability based on partitions of the set of observables, rather than on particle tensor products. In this way, the characterizing properties of nonseparable fermion states can be explicitly analyzed, allowing a precise description of the geometric structure of the corresponding state space. These results have direct applications in fermion quantum metrology: Sub-shot-noise accuracy in parameter estimation can be obtained without the need of a preliminary state entangling operation.

  3. Fermion localization on a split brane

    SciTech Connect

    Chumbes, A. E. R.; Vasquez, A. E. O.; Hott, M. B.

    2011-05-15

    In this work we analyze the localization of fermions on a brane embedded in five-dimensional, warped and nonwarped, space-time. In both cases we use the same nonlinear theoretical model with a nonpolynomial potential featuring a self-interacting scalar field whose minimum energy solution is a soliton (a kink) which can be continuously deformed into a two-kink. Thus a single brane splits into two branes. The behavior of spin 1/2 fermions wave functions on the split brane depends on the coupling of fermions to the scalar field and on the geometry of the space-time.

  4. Two-dimensional fermionic Hong-Ou-Mandel interference with massless Dirac fermions

    NASA Astrophysics Data System (ADS)

    Khan, M. A.; Leuenberger, Michael N.

    2014-08-01

    We propose a two-dimensional Hong-Ou-Mandel (HOM) type interference experiment for massless Dirac fermions in graphene and 3D topological insulators. Since massless Dirac fermions exhibit linear dispersion, similar to photons in vacuum, they can be used to obtain the HOM interference intensity pattern as a function of the delay time between two massless Dirac fermions. We show that while the Coulomb interaction leads to a significant change in the angle dependence of the tunneling of two identical massless Dirac fermions incident from opposite sides of a potential barrier, it does not affect the HOM interference pattern. We apply our formalism to develop a massless Dirac fermion beam splitter (BS) for controlling the transmission and reflection coefficients. We calculate the resulting time-resolved correlation function for two identical massless Dirac fermions scattering off the BS.

  5. Fermionic Schwinger effect and induced current in de Sitter space

    SciTech Connect

    Hayashinaka, Takahiro; Fujita, Tomohiro; Yokoyama, Jun’ichi

    2016-07-08

    We explore Schwinger effect of spin 1/2 charged particles with static electric field in 1+3 dimensional de Sitter spacetime. We analytically calculate the vacuum expectation value of the spinor current which is induced by the produced particles in the electric field. The renormalization is performed with the adiabatic subtraction scheme. We find that the current becomes negative, namely it flows in the direction opposite to the electric field, if the electric field is weaker than a certain threshold value depending on the fermion mass, which is also known to happen in the case of scalar charged particles in 1+3 de Sitter spacetime. Contrary to the scalar case, however, the IR hyperconductivity is absent in the spinor case.

  6. General form of the boson-fermion interaction in the interacting boson-fermion model-2

    NASA Astrophysics Data System (ADS)

    Matus, F. A.; Barea, J.

    2017-03-01

    The boson-fermion interaction in the interacting boson-fermion model-2 (IBFM-2) is derived in a systematic and general form from a quadrupole-quadrupole force using several nondegenerate levels. The boson-fermion quadrupole operator employed is obtained from the boson-fermion image of the one nucleon transfer operator which in turn can be calculated following two alternative schemes: the Otsuka-Arima-Iachello and generalized Holstein-Primakoff schemes. Four different terms (two quadrupole and two exchange) were obtained. Application of the new expressions to a single-j model is studied and analyzed.

  7. Kondo lattice and antiferromagnetic behavior in quaternary CeTAl4Si2 (T = Rh, Ir) single crystals

    DOE PAGES

    Maurya, Arvind; Kulkarni, Ruta; Thamizhavel, Arumugam; ...

    2016-02-26

    Here, we have explored in detail the anisotropic magnetic properties of CeRhAl4Si2 and CeIrAl4Si2, which undergo two antiferromagnetic transitions, at TN1 = 12.6 and 15.5 K, followed by a second transition at TN2 = 9.4 and 13.8 K, respectively, with the [001]-axis as the relatively easy axis of magnetization. The electrical resistivity at ambient and applied pressure provides evidence of Kondo interaction in both compounds, further supported by a reduced value of the entropy associated with the magnetic ordering. The Sommerfeld coefficient γ is inferred to be 195.6 and 49.4 mJ/(mol K2) for CeRhAl4Si2 and CeIrAl4Si2, respectively, classifying these materialsmore » as moderate heavy-fermion compounds. The crystal electric field energy levels are derived from the peak seen in the Schottky heat capacity. Furthermore, we have also performed electronic structure calculations by using the local spin density approximation + U [LSDA+U] approach, which provide physical insights on the observed magnetic behavior of these two compounds.« less

  8. Amplified fermion production from overpopulated Bose fields

    NASA Astrophysics Data System (ADS)

    Berges, J.; Gelfand, D.; Sexty, D.

    2014-01-01

    We study the real-time dynamics of fermions coupled to scalar fields in a linear sigma model, which is often employed in the context of preheating after inflation or as a low-energy effective model for quantum chromodynamics. We find a dramatic amplification of fermion production in the presence of highly occupied bosonic quanta for weak as well as strong effective couplings. For this we consider the range of validity of different methods: lattice simulations with male/female fermions, the mode functions approach and the quantum 2PI effective action with its associated kinetic theory. For strongly coupled fermions we find a rapid approach to a Fermi-Dirac distribution with time-dependent temperature and chemical potential parameters, while the bosons are still far from equilibrium.

  9. Fermionic Orbital Optimization in Tensor Network States

    NASA Astrophysics Data System (ADS)

    Krumnow, C.; Veis, L.; Legeza, Ö.; Eisert, J.

    2016-11-01

    Tensor network states and specifically matrix-product states have proven to be a powerful tool for simulating ground states of strongly correlated spin models. Recently, they have also been applied to interacting fermionic problems, specifically in the context of quantum chemistry. A new freedom arising in such nonlocal fermionic systems is the choice of orbitals, it being far from clear what choice of fermionic orbitals to make. In this Letter, we propose a way to overcome this challenge. We suggest a method intertwining the optimization over matrix product states with suitable fermionic Gaussian mode transformations. The described algorithm generalizes basis changes in the spirit of the Hartree-Fock method to matrix-product states, and provides a black box tool for basis optimization in tensor network methods.

  10. Thermostatistics of bosonic and fermionic Fibonacci oscillators

    NASA Astrophysics Data System (ADS)

    Algin, Abdullah; Arik, Metin; Senay, Mustafa; Topcu, Gozde

    2017-01-01

    In this work, we first introduce some new properties concerning the Fibonacci calculus. We then discuss the thermostatistics of gas models of two-parameter deformed oscillators, called bosonic and fermionic Fibonacci oscillators, in the thermodynamical limit. In this framework, we analyze the behavior of two-parameter deformed mean occupation numbers describing the Fibonacci-type bosonic and fermionic intermediate-statistics particles. A virial expansion of the equation of state for the bosonic Fibonacci oscillators’ gas model is obtained in both two and three dimensions, and the first five virial coefficients are derived in terms of the real independent deformation parameters p and q. The effect of bosonic and fermionic p, q-deformation on the thermostatistical properties of Fibonacci-type p, q-boson and p, q-fermion gas models are also discussed. The results obtained in this work can be useful for investigating some exotic quasiparticle states encountered in condensed matter systems.

  11. Quantum-Gas Microscope for Fermionic Atoms

    NASA Astrophysics Data System (ADS)

    Cheuk, Lawrence W.; Nichols, Matthew A.; Okan, Melih; Gersdorf, Thomas; Ramasesh, Vinay V.; Bakr, Waseem S.; Lompe, Thomas; Zwierlein, Martin W.

    2015-05-01

    We realize a quantum-gas microscope for fermionic 40K atoms trapped in an optical lattice, which allows one to probe strongly correlated fermions at the single-atom level. We combine 3D Raman sideband cooling with high-resolution optics to simultaneously cool and image individual atoms with single-lattice-site resolution at a detection fidelity above 95%. The imaging process leaves the atoms predominantly in the 3D motional ground state of their respective lattice sites, inviting the implementation of a Maxwell's demon to assemble low-entropy many-body states. Single-site-resolved imaging of fermions enables the direct observation of magnetic order, time-resolved measurements of the spread of particle correlations, and the detection of many-fermion entanglement.

  12. Fermion localization in a backreacted warped spacetime

    NASA Astrophysics Data System (ADS)

    Paul, Tanmoy; SenGupta, Soumitra

    2017-06-01

    We consider a five dimensional anti-de Sitter (AdS) warped spacetime in presence of a massive scalar field in the bulk. The scalar field potential fulfills the requirement of modulus stabilization even when the effect of backreaction of the stabilizing field is taken into account. In such a scenario, we explore the role of backreaction on the localization of bulk fermions which in turn determines the effective radion-fermion coupling on the brane. Our result reveals that both the chiral modes of the zeroth Kaluza-Klein (KK) fermions get localized near TeV brane as the backreaction of the scalar field increases. We also show that the profile of massive KK fermions shifts towards the Planck brane with an increasing backreaction parameter. Some implications in the context of LHC physics are discussed.

  13. Factorization of fermion doubles on the lattice

    NASA Astrophysics Data System (ADS)

    de A. Bicudo, P. J.

    2000-04-01

    We address the problem of the fermion species doubling on the Lattice. Our strategy is to factorize the fermion doubles from the action. The mass term of the Dirac-Wilson action is changed. In this case the extra roots which appear in the action of free fermions in the moment representation are independent of the mass and can be factorized from the fermion propagator. However the gauge couplings suffer from the pathological ghost poles which are common to non-local actions. This action can be used to find a solution of the Ginsparg Wilson relation, which is cured from the non-local pathology. Finally we compare this factorized action with solutions of The Ginsparg Wilson relation. We find that the present is equivalent to the Zenkin action, and that it is not exponentially local, in contrast with Neuberger's action.

  14. Majorana Fermions and Topology in Superconductors

    NASA Astrophysics Data System (ADS)

    Sato, Masatoshi; Fujimoto, Satoshi

    2016-07-01

    Topological superconductors are novel classes of quantum condensed phases, characterized by topologically nontrivial structures of Cooper pairing states. On the surfaces of samples and in vortex cores of topological superconductors, Majorana fermions, which are particles identified with their own anti-particles, appear as Bogoliubov quasiparticles. The existence and stability of Majorana fermions are ensured by bulk topological invariants constrained by the symmetries of the systems. Majorana fermions in topological superconductors obey a new type of quantum statistics referred to as non-Abelian statistics, which is distinct from bose and fermi statistics, and can be utilized for application to topological quantum computation. Also, Majorana fermions give rise to various exotic phenomena such as "fractionalization", non-local correlation, and "teleportation". A pedagogical review of these subjects is presented. We also discuss interaction effects on topological classification of superconductors, and the basic properties of Weyl superconductors.

  15. Bilinear forms on fermionic Novikov algebras

    NASA Astrophysics Data System (ADS)

    Chen, Zhiqi; Zhu, Fuhai

    2007-05-01

    Novikov algebras were introduced in connection with the Poisson brackets of hydrodynamic type and Hamiltonian operators in formal variational calculus. Fermionic Novikov algebras correspond to a certain Hamiltonian super-operator in a super-variable. In this paper, we show that there is a remarkable geometry on fermionic Novikov algebras with non-degenerate invariant symmetric bilinear forms, which we call pseudo-Riemannian fermionic Novikov algebras. They are related to pseudo-Riemannian Lie algebras. Furthermore, we obtain a procedure to classify pseudo-Riemannian fermionic Novikov algebras. As an application, we give the classification in dimension <=4. Motivated by the one in dimension 4, we construct some examples in high dimensions.

  16. Two-photon interactions with Majorana fermions

    NASA Astrophysics Data System (ADS)

    Latimer, David C.

    2016-11-01

    Because Majorana fermions are their own antiparticles, their electric and magnetic dipole moments must vanish, leaving the anapole moment as their only static electromagnetic property. But the existence of induced dipole moments is not necessarily prohibited. Through a study of real Compton scattering, we explore the constraints that the Majorana fermion's self-conjugate nature has on induced moments. In terms of the Compton amplitude, we find no constraints if the interactions are separately invariant under charge conjugation, parity, and time reversal. However, if the interactions are odd under parity and even under time reversal, then these contributions to the Compton amplitude must vanish. We employ a simple model to confirm these general findings via explicit calculation of the Majorana fermion's polarizabilities. We then use these polarizabilities to estimate the cross section for s -wave annihilation of two Majorana fermions into photons. The cross section is larger than a naive estimate might suggest.

  17. Canonical approach to Ginsparg-Wilson fermions

    SciTech Connect

    Matsui, Kosuke; Okamoto, Tomohito; Fujiwara, Takanori

    2005-06-01

    Based upon the lattice Dirac operator satisfying the Ginsparg-Wilson relation, we investigate canonical formulation of massless fermion on the spatial lattice. For free fermion system exact chiral symmetry can be implemented without species doubling. In the presence of gauge couplings the chiral symmetry is violated. We show that the divergence of the axial vector current is related to the chiral anomaly in the classical continuum limit.

  18. Evolution of boson-fermion stars

    NASA Astrophysics Data System (ADS)

    Valdez-Alvarado, Susana; Palenzuela, Carlos; Alic, Daniela; Ureña-López, L. Arturo; Becerril, Ricardo

    2012-08-01

    The boson-fermion stars can be modeled with a complex scalar field coupled minimally to a perfect fluid (i.e., without viscosity and non-dissipative). We present a study of these solutions and their dynamical evolution by solving numerically the Einstein-Klein-Gordon-Hydrodynamic (EKGHD) system. It is shown that stable configurations exist, but stability of general configurations depends finely upon the number of bosons and fermions.

  19. Inhomogeneous state of few-fermion superfluids.

    PubMed

    Bugnion, P O; Lofthouse, J A; Conduit, G J

    2013-07-26

    The few-fermion atomic gas is an ideal setting to explore inhomogeneous superfluid pairing analogous to the Larkin-Ovchinnikov state. Two up and one down-spin atom is the minimal configuration that displays an inhomogeneous pairing density, whereas imbalanced systems containing more fermions present a more complex pairing topology. With more than eight atoms trapped the system approaches the macroscopic superfluid limit. An oblate trap with a central barrier offers a direct experimental probe of pairing inhomogeneity.

  20. Fermionic topological quantum states as tensor networks

    NASA Astrophysics Data System (ADS)

    Wille, C.; Buerschaper, O.; Eisert, J.

    2017-06-01

    Tensor network states, and in particular projected entangled pair states, play an important role in the description of strongly correlated quantum lattice systems. They do not only serve as variational states in numerical simulation methods, but also provide a framework for classifying phases of quantum matter and capture notions of topological order in a stringent and rigorous language. The rapid development in this field for spin models and bosonic systems has not yet been mirrored by an analogous development for fermionic models. In this work, we introduce a tensor network formalism capable of capturing notions of topological order for quantum systems with fermionic components. At the heart of the formalism are axioms of fermionic matrix-product operator injectivity, stable under concatenation. Building upon that, we formulate a Grassmann number tensor network ansatz for the ground state of fermionic twisted quantum double models. A specific focus is put on the paradigmatic example of the fermionic toric code. This work shows that the program of describing topologically ordered systems using tensor networks carries over to fermionic models.

  1. Fermion-induced quantum critical points.

    PubMed

    Li, Zi-Xiang; Jiang, Yi-Fan; Jian, Shao-Kai; Yao, Hong

    2017-08-22

    A unified theory of quantum critical points beyond the conventional Landau-Ginzburg-Wilson paradigm remains unknown. According to Landau cubic criterion, phase transitions should be first-order when cubic terms of order parameters are allowed by symmetry in the Landau-Ginzburg free energy. Here, from renormalization group analysis, we show that second-order quantum phase transitions can occur at such putatively first-order transitions in interacting two-dimensional Dirac semimetals. As such type of Landau-forbidden quantum critical points are induced by gapless fermions, we call them fermion-induced quantum critical points. We further introduce a microscopic model of SU(N) fermions on the honeycomb lattice featuring a transition between Dirac semimetals and Kekule valence bond solids. Remarkably, our large-scale sign-problem-free Majorana quantum Monte Carlo simulations show convincing evidences of a fermion-induced quantum critical points for N = 2, 3, 4, 5 and 6, consistent with the renormalization group analysis. We finally discuss possible experimental realizations of the fermion-induced quantum critical points in graphene and graphene-like materials.Quantum phase transitions are governed by Landau-Ginzburg theory and the exceptions are rare. Here, Li et al. propose a type of Landau-forbidden quantum critical points induced by gapless fermions in two-dimensional Dirac semimetals.

  2. Quantum Gas Microscope for Fermionic Atoms

    NASA Astrophysics Data System (ADS)

    Okan, Melih; Cheuk, Lawrence; Nichols, Matthew; Lawrence, Katherine; Zhang, Hao; Zwierlein, Martin

    2016-05-01

    Strongly interacting fermions define the properties of complex matter throughout nature, from atomic nuclei and modern solid state materials to neutron stars. Ultracold atomic Fermi gases have emerged as a pristine platform for the study of many-fermion systems. In this poster we demonstrate the realization of a quantum gas microscope for fermionic 40 K atoms trapped in an optical lattice and the recent experiments which allows one to probe strongly correlated fermions at the single atom level. We combine 3D Raman sideband cooling with high- resolution optics to simultaneously cool and image individual atoms with single lattice site resolution at a detection fidelity above 95%. The imaging process leaves the atoms predominantly in the 3D motional ground state of their respective lattice sites, inviting the implementation of a Maxwell's demon to assemble low-entropy many-body states. Single-site resolved imaging of fermions enables the direct observation of magnetic order, time resolved measurements of the spread of particle correlations, and the detection of many-fermion entanglement. NSF, AFOSR-PECASE, AFOSR-MURI on Exotic Phases of Matter, ARO-MURI on Atomtronics, ONR, a Grant from the Army Research Office with funding from the DARPA OLE program, and the David and Lucile Packard Foundation.

  3. Fermion number violating effects in low scale leptogenesis

    NASA Astrophysics Data System (ADS)

    Eijima, Shintaro; Shaposhnikov, Mikhail

    2017-08-01

    The existence of baryon asymmetry and dark matter in the Universe may be related to CP-violating reactions of three heavy neutral leptons (HNLs) with masses well below the Fermi scale. The dynamical description of the lepton asymmetry generation, which is the key ingredient of baryogenesis and of dark matter production, is quite complicated due to the presence of many different relaxation time scales and the necessity to include quantum-mechanical coherent effects in HNL oscillations. We derive kinetic equations accounting for fermion number violating effects missed so far and identify one of the domains of HNL masses that can potentially lead to large lepton asymmetry generation boosting the sterile neutrino dark matter production.

  4. Lattice simulations with eight flavors of domain wall fermions in SU(3) gauge theory

    NASA Astrophysics Data System (ADS)

    Appelquist, T.; Brower, R. C.; Fleming, G. T.; Kiskis, J.; Lin, M. F.; Neil, E. T.; Osborn, J. C.; Rebbi, C.; Rinaldi, E.; Schaich, D.; Schroeder, C.; Syritsyn, S.; Voronov, G.; Vranas, P.; Weinberg, E.; Witzel, O.; Lattice Strong Dynamics LSD Collaboration

    2014-12-01

    We study an SU(3) gauge theory with Nf=8 degenerate flavors of light fermions in the fundamental representation. Using the domain wall fermion formulation, we investigate the light hadron spectrum, chiral condensate ⟨ψ ¯ ψ ⟩ and electroweak S parameter. We consider a range of light fermion masses on two lattice volumes at a single gauge coupling chosen so that IR scales approximately match those from our previous studies of the two- and six-flavor systems. Our results for the Nf=8 spectrum suggest spontaneous chiral symmetry breaking, though fits to the fermion mass dependence of spectral quantities do not strongly disfavor the hypothesis of mass-deformed infrared conformality. Compared to Nf=2 we observe a significant enhancement of ⟨ψ ¯ψ ⟩ relative to the symmetry breaking scale F , similar to the situation for Nf=6 . The reduction of the S parameter, related to parity doubling in the vector and axial-vector channels, is also comparable to our six-flavor results.

  5. The one step fermionic ladder

    NASA Astrophysics Data System (ADS)

    Das, Joy Prakash; Setlur, Girish S.

    2017-10-01

    The one step fermionic ladder refers to two parallel Luttinger Liquids (poles of the ladder) placed such that there is a finite probability of electrons hopping between the two poles at a pair of opposing points along each of the poles. The many-body Green function for such a system is calculated in presence of forward scattering interactions using the powerful non-chiral bosonization technique (NCBT). This technique is based on a non-standard harmonic analysis of the rapidly varying parts of the density fields appropriate for the study of strongly inhomogeneous ladder systems. The closed analytical expression for the correlation function obtained from NCBT is nothing but the series involving the RPA (Random Phase Approximation) diagrams in powers of the forward scattering coupling strength resummed to include only the most singular terms with the source of inhomogeneities treated exactly. Finally the correlation functions are used to study physical phenomena such as Friedel oscillations and the conductance of such systems with the potential difference applied across various ends.

  6. Iterants, Fermions and Majorana Operators

    NASA Astrophysics Data System (ADS)

    Kauffman, Louis H.

    Beginning with an elementary, oscillatory discrete dynamical system associated with the square root of minus one, we study both the foundations of mathematics and physics. Position and momentum do not commute in our discrete physics. Their commutator is related to the diffusion constant for a Brownian process and to the Heisenberg commutator in quantum mechanics. We take John Wheeler's idea of It from Bit as an essential clue and we rework the structure of that bit to a logical particle that is its own anti-particle, a logical Marjorana particle. This is our key example of the amphibian nature of mathematics and the external world. We show how the dynamical system for the square root of minus one is essentially the dynamics of a distinction whose self-reference leads to both the fusion algebra and the operator algebra for the Majorana Fermion. In the course of this, we develop an iterant algebra that supports all of matrix algebra and we end the essay with a discussion of the Dirac equation based on these principles.

  7. Rooting issue for a lattice fermion formulation similar to staggered fermions but without taste mixing

    SciTech Connect

    Adams, David H.

    2008-05-15

    To investigate the viability of the 4th root trick for the staggered fermion determinant in a simpler setting, we consider a 2-taste (flavor) lattice fermion formulation with no taste mixing but with exact taste-nonsinglet chiral symmetries analogous to the taste-nonsinglet U(1){sub A} symmetry of staggered fermions. Creutz's objections to the rooting trick apply just as much in this setting. To counter them we show that the formulation has robust would-be zero modes in topologically nontrivial gauge backgrounds, and that these manifest themselves in a viable way in the rooted fermion determinant and also in the disconnected piece of the pseudoscalar meson propagator as required to solve the U(1) problem. Also, our rooted theory is heuristically seen to be in the right universality class for QCD if the same is true for an unrooted mixed fermion action theory.

  8. Fermionic entanglement that survives a black hole

    SciTech Connect

    Martin-Martinez, Eduardo; Leon, Juan

    2009-10-15

    We introduce an arbitrary number of accessible modes when analyzing bipartite entanglement degradation due to Unruh effect between two partners Alice and Rob. Under the single mode approximation (SMA) a fermion field only had a few accessible levels due to Pauli exclusion principle conversely to bosonic fields which had an infinite number of excitable levels. This was argued to justify entanglement survival in the fermionic case in the SMA infinite acceleration limit. Here we relax SMA. Hence, an infinite number of modes are excited as the observer Rob accelerates, even for a fermion field. We will prove that, despite this analogy with the bosonic case, entanglement loss is limited. We will show that this comes from fermionic statistics through the characteristic structure it imposes on the infinite dimensional density matrix for Rob. Surprisingly, the surviving entanglement is independent of the specific maximally entangled state chosen, the kind of fermionic field analyzed, and the number of accessible modes considered. We shall discuss whether this surviving entanglement goes beyond the purely statistical correlations, giving insight concerning the black hole information paradox.

  9. Spectrum structure of a fermion on Bloch branes with two scalar-fermion couplings

    NASA Astrophysics Data System (ADS)

    Xie, Qun-Ying; Guo, Heng; Zhao, Zhen-Hua; Du, Yun-Zhi; Zhang, Yu-Peng

    2017-03-01

    It is known that the Bloch brane is generated by an odd scalar field ϕ and an even one χ. In order to localize a bulk fermion on the Bloch brane, the coupling between the fermion and scalars should be introduced. There are two localization mechanisms in the literature, the Yukawa coupling -η \\bar{\\Psi}{{F}1}≤ft(φ,χ \\right) \\Psi and non-Yukawa coupling λ \\bar{\\Psi}{ΓM}{{\\partial}M}{{F}2}≤ft(φ,χ \\right){γ5} \\Psi . The Yukawa coupling has been considered. In this paper, we consider both couplings between the fermion and the scalars with {{F}1}={χm}{φ2p+1} and {{F}2}={χn}{φ2q} , and investigate the localization and spectrum structure of the fermion on the Bloch brane. It is found that the left-handed fermion zero mode can be localized on the Bloch brane under some conditions, and the effective potentials have rich structure and may be volcano-like, finite square well-like, and infinite potentials. As a result, the spectrum consists of a series of resonant Kaluza-Klein fermions, finite or infinite numbers of bound Kaluza-Klein fermions. Especially, we find a new feature of the introduction of both couplings: the spectrum for the case of finite square well-like potentials contains discrete quasi-localized and localized massive KK modes simultaneously.

  10. Simulation of strongly correlated fermions in two spatial dimensions with fermionic projected entangled-pair states

    NASA Astrophysics Data System (ADS)

    Corboz, Philippe; Orús, Román; Bauer, Bela; Vidal, Guifré

    2010-04-01

    We explain how to implement, in the context of projected entangled-pair states (PEPSs), the general procedure of fermionization of a tensor network introduced in P. Corboz and G. Vidal, Phys. Rev. B 80, 165129 (2009). The resulting fermionic PEPS, similar to previous proposals, can be used to study the ground state of interacting fermions on a two-dimensional lattice. As in the bosonic case, the cost of simulations depends on the amount of entanglement in the ground state and not directly on the strength of interactions. The present formulation of fermionic PEPS leads to a straightforward numerical implementation that allowed us to recycle much of the code for bosonic PEPS. We demonstrate that fermionic PEPS are a useful variational ansatz for interacting fermion systems by computing approximations to the ground state of several models on an infinite lattice. For a model of interacting spinless fermions, ground state energies lower than Hartree-Fock results are obtained, shifting the boundary between the metal and charge-density wave phases. For the t-J model, energies comparable with those of a specialized Gutzwiller-projected ansatz are also obtained.

  11. Quantum Phases of Fermionic Cold Atoms Through Pairing and Dissociation

    NASA Astrophysics Data System (ADS)

    Lopez, Nicolas; Tsai, Shan-Wen; Timmermans, E.; Lin, Chi-Yong

    2011-03-01

    Cold atom experiments have realized molecule creation consisting of paired fermions and dissociation of weakly bound molecules into correlated fermions by tuning of the interactions with external fields [1,2]. We study many-body correlations in such system where molecules are weakly bound and therefore pairs of fermionic atoms convert into and dissociate from the bound molecule state. This exchange mediates a long-range interaction between the fermions. We consider a simple many-body Hamiltonian that includes the destruction of fermionic atom pairs to form single bosonic molecules and vice versa. We employ a functional renormalization-group approach to search for instabilities from the disordered quantum liquid phase that may arise from a boson mediated fermion-fermion interaction. We calculate the renormalized frequency-dependent fermion interactions vertices and renormalized molecular binding energy.

  12. Plaquette boson-fermion model of cuprates

    NASA Astrophysics Data System (ADS)

    Altman, Ehud; Auerbach, Assa

    2002-03-01

    The strongly interacting Hubbard model on the square lattice is reduced to the low energy plaquette boson fermion model (PBFM). The four bosons (an antiferromagnon triplet and a d-wave hole pair), and the fermions are defined by the lowest plaquette eigenstates. We apply the contractor renormalization method of Morningstar and Weinstein to compute the boson effective interactions. The range-3 truncation error is found to be very small, signaling short hole-pair and magnon coherence lengths. The pair-hopping and magnon interactions are comparable, which explains the rapid destruction of antiferromagnetic order with emergence of superconductivity, and validates a key assumption of the projected SO(5) theory. A vacuum crossing at larger doping marks a transition into the overdoped regime. With hole fermions occupying small Fermi pockets and Andreev coupled to hole pair bosons, the PBFM yields several testable predictions for photoemission, tunneling asymmetry, and entropy measurements.

  13. Fermionic light in common optical media.

    PubMed

    Novoa, David; Michinel, Humberto; Tommasini, Daniele

    2010-11-12

    Recent experiments have proved that the response to short laser pulses of common optical media, such as air or oxygen, can be described by focusing Kerr and higher order nonlinearities of alternating signs. Such media support the propagation of steady solitary waves. We argue by both numerical and analytical computations that the low-power fundamental bright solitons satisfy an equation of state which is similar to that of a degenerate gas of fermions at zero temperature. Considering, in particular, the propagation in both O2 and air, we also find that the high-power solutions behave like droplets of ordinary liquids. We then show how a grid of the fermionic light bubbles can be generated and forced to merge in a liquid droplet. This leads us to propose a set of experiments aimed at the production of both the fermionic and liquid phases of light, and at the demonstration of the transition from the former to the latter.

  14. Dirac fermions in an antiferromagnetic semimetal

    SciTech Connect

    Tang, Peizhe; Zhou, Quan; Xu, Gang; Zhang, Shou-Cheng

    2016-08-08

    Analogues of the elementary particles have been extensively searched for in condensed-matter systems for both scientific interest and technological applications. Recently, massless Dirac fermions were found to emerge as low-energy excitations in materials now known as Dirac semimetals. All of the currently known Dirac semimetals are non-magnetic with both time-reversal symmetry and inversion symmetry. Here in this paper, we show that Dirac fermions can exist in one type of antiferromagnetic system, where both and are broken but their combination is respected. We propose orthorhombic antiferromagnet CuMnAs as a candidate, analyse the robustness of the Dirac points under symmetry protections and demonstrate its distinctive bulk dispersions, as well as the corresponding surface states, by ab initio calculations. Our results provide a possible platform to study the interplay of Dirac fermion physics and magnetism.

  15. Fermions on one or fewer kinks

    SciTech Connect

    Chu Yizen; Vachaspati, Tanmay

    2008-01-15

    We find the full spectrum of fermion bound states on a Z{sub 2} kink. In addition to the zero mode, there are int[2m{sub f}/m{sub s}] bound states, where m{sub f} is the fermion and m{sub s} the scalar mass. We also study fermion modes on the background of a well-separated kink-antikink pair. Using a variational argument, we prove that there is at least one bound state in this background, and that the energy of this bound state goes to zero with increasing kink-antikink separation, 2L, and faster than e{sup -a2L} where a=min(m{sub s},2m{sub f}). By numerical evaluation, we find some of the low lying bound states explicitly.

  16. Ladder physics in the spin fermion model

    DOE PAGES

    Tsvelik, A. M.

    2017-05-01

    A link is established between the spin fermion (SF) model of the cuprates and the approach based on the analogy between the physics of doped Mott insulators in two dimensions and the physics of fermionic ladders. This enables one to use nonperturbative results derived for fermionic ladders to move beyond the large-N approximation in the SF model. Here, it is shown that the paramagnon exchange postulated in the SF model has exactly the right form to facilitate the emergence of the fully gapped d-Mott state in the region of the Brillouin zone at the hot spots of the Fermi surface.more » Hence, the SF model provides an adequate description of the pseudogap.« less

  17. Dirac fermions in an antiferromagnetic semimetal

    DOE PAGES

    Tang, Peizhe; Zhou, Quan; Xu, Gang; ...

    2016-08-08

    Analogues of the elementary particles have been extensively searched for in condensed-matter systems for both scientific interest and technological applications. Recently, massless Dirac fermions were found to emerge as low-energy excitations in materials now known as Dirac semimetals. All of the currently known Dirac semimetals are non-magnetic with both time-reversal symmetry and inversion symmetry. Here in this paper, we show that Dirac fermions can exist in one type of antiferromagnetic system, where both and are broken but their combination is respected. We propose orthorhombic antiferromagnet CuMnAs as a candidate, analyse the robustness of the Dirac points under symmetry protections andmore » demonstrate its distinctive bulk dispersions, as well as the corresponding surface states, by ab initio calculations. Our results provide a possible platform to study the interplay of Dirac fermion physics and magnetism.« less

  18. Dirac fermions in an antiferromagnetic semimetal

    NASA Astrophysics Data System (ADS)

    Tang, Peizhe; Zhou, Quan; Xu, Gang; Zhang, Shou-Cheng

    2016-12-01

    Analogues of the elementary particles have been extensively searched for in condensed-matter systems for both scientific interest and technological applications. Recently, massless Dirac fermions were found to emerge as low-energy excitations in materials now known as Dirac semimetals. All of the currently known Dirac semimetals are non-magnetic with both time-reversal symmetry and inversion symmetry . Here we show that Dirac fermions can exist in one type of antiferromagnetic system, where both and are broken but their combination is respected. We propose orthorhombic antiferromagnet CuMnAs as a candidate, analyse the robustness of the Dirac points under symmetry protections and demonstrate its distinctive bulk dispersions, as well as the corresponding surface states, by ab initio calculations. Our results provide a possible platform to study the interplay of Dirac fermion physics and magnetism.

  19. Fermion boson metamorphosis in field theory

    SciTech Connect

    Ha, Y.K.

    1982-01-01

    In two-dimensional field theories many features are especially transparent if the Fermi fields are represented by non-local expressions of the Bose fields. Such a procedure is known as boson representation. Bilinear quantities appear in the Lagrangian of a fermion theory transform, however, as simple local expressions of the bosons so that the resulting theory may be written as a theory of bosons. Conversely, a theory of bosons may be transformed into an equivalent theory of fermions. Together they provide a basis for generating many interesting equivalences between theories of different types. In the present work a consistent scheme for constructing a canonical Fermi field in terms of a real scalar field is developed and such a procedure is valid and consistent with the tenets of quantum field theory is verified. A boson formulation offers a unifying theme in understanding the structure of many theories. This is illustrated by the boson formulation of a multifermion theory with chiral and internal symmetries. The nature of dynamical generation of mass when the theory undergoes boson transmutation and the preservation of continuous chiral symmetry in the massive case are examined. The dynamics of the system depends to a great extent on the specific number of fermions and different models of the same system can have very different properties. Many unusual symmetries of the fermion theory, such as hidden symmetry, duality and triality symmetries, are only manifest in the boson formulation. The underlying connections between some models with U(N) internal symmetry and another class of fermion models built with Majorana fermions which have O(2N) internal symmetry are uncovered.

  20. Scaling of fat-link irrelevant-clover fermions

    SciTech Connect

    Zanotti, J.M.; Lasscock, B.; Leinweber, D.B.; Williams, A.G.

    2005-02-01

    Hadron masses are calculated in quenched lattice QCD on a variety of lattices in order to probe the scaling behavior of the Fat-Link Irrelevant Clover (FLIC) fermion action, a fat-link clover fermion action in which the purely irrelevant operators of the fermion action are constructed using APE-smeared links. The scaling analysis indicates FLIC fermions provide a new form of nonperturbative O(a) improvement where near-continuum results are obtained at finite lattice spacing.

  1. Topological susceptibility in staggered fermion chiral perturbation theory

    SciTech Connect

    Billeter, Brian; DeTar, Carleton; Osborn, James

    2004-10-01

    The topological susceptibility of the vacuum in quantum chromodynamics has been simulated numerically using the Asqtad improved staggered fermion formalism. At nonzero lattice spacing, the residual fermion doublers (fermion tastes) in the staggered fermion formalism give contributions to the susceptibility that deviate from conventional continuum chiral perturbation theory. In this brief report, we estimate the taste-breaking artifact and compare it with results of recent simulations, finding that it accounts for roughly half of the scaling violation.

  2. Fermion-fermion scattering in quantum field theory with superconducting circuits.

    PubMed

    García-Álvarez, L; Casanova, J; Mezzacapo, A; Egusquiza, I L; Lamata, L; Romero, G; Solano, E

    2015-02-20

    We propose an analog-digital quantum simulation of fermion-fermion scattering mediated by a continuum of bosonic modes within a circuit quantum electrodynamics scenario. This quantum technology naturally provides strong coupling of superconducting qubits with a continuum of electromagnetic modes in an open transmission line. In this way, we propose qubits to efficiently simulate fermionic modes via digital techniques, while we consider the continuum complexity of an open transmission line to simulate the continuum complexity of bosonic modes in quantum field theories. Therefore, we believe that the complexity-simulating-complexity concept should become a leading paradigm in any effort towards scalable quantum simulations.

  3. Floquet Majorana Fermions for Topological Qubits

    NASA Astrophysics Data System (ADS)

    Liu, D. E.; Levchenko, A.; Baranger, H. U.

    2013-03-01

    We develop an approach to realizing a topological phase transition and non-Abelian statistics with dynamically induced Floquet Majorana Fermions (FMFs). When the periodic driving potential does not break fermion parity conservation, FMFs can encode quantum information. Quasi-energy analysis shows that a stable FMF zero mode and two other satellite modes exist in a wide parameter space with large quasi-energy gaps, which prevents transitions to other Floquet states under adiabatic driving. We also show that in the asymptotic limit FMFs preserve non-Abelian statistics and, thus, behave like their equilibrium counterparts.

  4. Cosmic expansion from boson and fermion fields

    NASA Astrophysics Data System (ADS)

    de Souza, Rudinei C.; Kremer, Gilberto M.

    2011-06-01

    This paper consists in analyzing an action that describes boson and fermion fields minimally coupled to the gravity and a common matter field. The self-interaction potentials of the fields are not chosen a priori but from the Noether symmetry approach. The Noether forms of the potentials allow the boson field to play the role of dark energy and matter and the fermion field to behave as standard matter. The constant of motion and the cyclic variable associated with the Noether symmetry allow the complete integration of the field equations, whose solution produces a universe with alternated periods of accelerated and decelerated expansion.

  5. Residual entanglement of accelerated fermions is useful

    NASA Astrophysics Data System (ADS)

    Farahmand, Mehrnoosh; Mohammadzadeh, Hosein; Rahimi, Robabeh; Mehri-Dehnavi, Hossein

    2017-08-01

    The non-vanishing residual entanglement, between the fermionic modes in the infinite acceleration limit, does not violate CHSH inequality, therefore it is not non-local. In this paper, we study the usefulness of the residual fermionic entanglement in single mode approximation and beyond single mode approximation. It is shown that there are some cases where the CHSH inequality is not violated by the residual entanglement, but the state is useful for quantum teleportation. Conditions for the violation of the CHSH inequality in terms of the ;presence probability; of the particle in different Rindler regions are given for the state to be useful for teleportation and superdense coding.

  6. Massless rotating fermions inside a cylinder

    SciTech Connect

    Ambruş, Victor E.; Winstanley, Elizabeth

    2015-12-07

    We study rotating thermal states of a massless quantum fermion field inside a cylinder in Minkowski space-time. Two possible boundary conditions for the fermion field on the cylinder are considered: the spectral and MIT bag boundary conditions. If the radius of the cylinder is sufficiently small, rotating thermal expectation values are finite everywhere inside the cylinder. We also study the Casimir divergences on the boundary. The rotating thermal expectation values and the Casimir divergences have different properties depending on the boundary conditions applied at the cylinder. This is due to the local nature of the MIT bag boundary condition, while the spectral boundary condition is nonlocal.

  7. Novel Fat-Link Fermion Actions

    SciTech Connect

    J. M. Zanotti; S. Bilson-Thompson; F. D. R. Bonnet; P. D. Coddington; D. B. Leinweber; A. G. Williams; J. B. Zhang; W. Melnitchouk; F. X. Lee

    2001-07-01

    The hadron mass spectrum is calculated in lattice QCD using a novel fat-link clover fermion action in which only the irrelevant operators in the fermion action are constructed using smeared links. The simulations are performed on a 16{sup 3} x 32 lattice with a lattice spacing of a=0.125 fm. We compare actions with n=4 and 12 smearing sweeps with a smearing fraction of 0.7. The n=4 Fat-Link Irrelevant Clover (FLIC) action provides scaling which is superior to mean-field improvement, and offers advantages over nonperturbative 0(a) improvement.

  8. Chiral gravitational waves from chiral fermions

    NASA Astrophysics Data System (ADS)

    Anber, Mohamed M.; Sabancilar, Eray

    2017-07-01

    We report on a new mechanism that leads to the generation of primordial chiral gravitational waves, and hence, the violation of the parity symmetry in the Universe. We show that nonperturbative production of fermions with a definite helicity is accompanied by the generation of chiral gravitational waves. This is a generic and model-independent phenomenon that can occur during inflation, reheating and radiation eras, and can leave imprints in the cosmic microwave background polarization and may be observed in future ground- and space-based interferometers. We also discuss a specific model where chiral gravitational waves are generated via the production of light chiral fermions during pseudoscalar inflation.

  9. Eigenenergies of fermions bound in Skyrme fields

    SciTech Connect

    Zhao, M. ); Hiller, J.R.

    1989-08-15

    A numerical method is applied to the calculation of bound-state energies of fermions in Skyrme fields. The models considered for the field are smoothed one- and two-step wells and a numerical approximation to the exact hedgehog soliton. The results for the smoothed wells confirm earlier work that showed the fermion spectrum to be sensitive to local variations in the Skyrme field. The spectrum for the hedgehog Skyrmion is similar to the spectra obtained by others for linear and exponential models.

  10. Pseudoscalar condensation induced by chiral anomaly and vorticity for massive fermions

    NASA Astrophysics Data System (ADS)

    Fang, Ren-hong; Pang, Jin-yi; Wang, Qun; Wang, Xin-nian

    2017-01-01

    We derive the pseudoscalar condensate induced by anomaly and vorticity from the Wigner function for massive fermions in homogeneous electromagnetic fields. It has an anomaly term and a force-vorticity coupling term. As a mass effect, the pseudoscalar condensate is linearly proportional to the fermion mass in small mass expansion. By a generalization to two-flavor and three-flavor cases, the neutral pion and eta meson condensates are calculated from the Wigner function and have anomaly parts as well as force-vorticity parts, in which the anomaly part of the neutral pion condensate is consistent with the previous result. We also discuss the possible observables of the condensates in heavy-ion collisions such as collective flows of neutral pions and eta mesons which may be influenced by the electromagnetic field and vorticity profiles.

  11. Minimal energy ensemble Monte Carlo algorithm for the partition function of fermions coupled to classical fields.

    PubMed

    Grzybowski, Przemysław R; Czekaj, Łukasz; Nogala, Mariusz; Ścibior, Adam; Chhajlany, Ravindra W

    2016-06-01

    Models of noninteracting fermions coupled to auxiliary classical fields are relevant to the understanding of a wide variety of problems in many-body physics, e.g., the description of manganites, diluted magnetic semiconductors, or strongly interacting electrons on lattices. We present a flat-histogram Monte Carlo algorithm that simulates a statistical ensemble that allows one to directly acquire the partition function at all temperatures for such systems. The defining feature of the algorithm is that it utilizes the complete thermodynamic information from the full energy spectrum of noninteracting fermions available during sampling of the configuration space of the classical fields. We benchmark the method for the classical Ising and Potts models in two dimensions, as well as the Falicov-Kimball model describing itinerant electrons interacting with heavy ions.

  12. Minimal energy ensemble Monte Carlo algorithm for the partition function of fermions coupled to classical fields

    NASA Astrophysics Data System (ADS)

    Grzybowski, Przemysław R.; Czekaj, Łukasz; Nogala, Mariusz; Ścibior, Adam; Chhajlany, Ravindra W.

    2016-06-01

    Models of noninteracting fermions coupled to auxiliary classical fields are relevant to the understanding of a wide variety of problems in many-body physics, e.g., the description of manganites, diluted magnetic semiconductors, or strongly interacting electrons on lattices. We present a flat-histogram Monte Carlo algorithm that simulates a statistical ensemble that allows one to directly acquire the partition function at all temperatures for such systems. The defining feature of the algorithm is that it utilizes the complete thermodynamic information from the full energy spectrum of noninteracting fermions available during sampling of the configuration space of the classical fields. We benchmark the method for the classical Ising and Potts models in two dimensions, as well as the Falicov-Kimball model describing itinerant electrons interacting with heavy ions.

  13. Fermionization and Mott-insulator formation in fermion trimers loaded in one-dimensional optical lattices

    NASA Astrophysics Data System (ADS)

    Gordillo, M. C.; De Soto, F.

    2017-07-01

    The behavior of small clusters of one spin-up and two spin-down fermions with unlike-spin repulsive interactions in one-dimensional optical lattices was calculated using a diffusion Monte Carlo technique. We considered also a harmonic potential in the longitudinal direction to make our system resemble the standard experimental setups. When the interparticle repulsion is strong enough, the onset of fermionization is observed irrespective of the optical lattice parameters considered, in line with previous results for pure harmonic confinement. However, fermionization can also be seen even for small interparticle couplings if the optical potential is deep enough. In addition, for certain values of the wavelengths and the potential depths defining the lattice, Mott insulators in the fermionization limit with only three atoms were found.

  14. Many-body formalism for fermions: The partition function

    NASA Astrophysics Data System (ADS)

    Watson, D. K.

    2017-09-01

    The partition function, a fundamental tenet in statistical thermodynamics, contains in principle all thermodynamic information about a system. It encapsulates both microscopic information through the quantum energy levels and statistical information from the partitioning of the particles among the available energy levels. For identical particles, this statistical accounting is complicated by the symmetry requirements of the allowed quantum states. In particular, for Fermi systems, the enforcement of the Pauli principle is typically a numerically demanding task, responsible for much of the cost of the calculations. The interplay of these three elements—the structure of the many-body spectrum, the statistical partitioning of the N particles among the available levels, and the enforcement of the Pauli principle—drives the behavior of mesoscopic and macroscopic Fermi systems. In this paper, we develop an approach for the determination of the partition function, a numerically difficult task, for systems of strongly interacting identical fermions and apply it to a model system of harmonically confined, harmonically interacting fermions. This approach uses a recently introduced many-body method that is an extension of the symmetry-invariant perturbation method (SPT) originally developed for bosons. It uses group theory and graphical techniques to avoid the heavy computational demands of conventional many-body methods which typically scale exponentially with the number of particles. The SPT application of the Pauli principle is trivial to implement since it is done "on paper" by imposing restrictions on the normal-mode quantum numbers at first order in the perturbation. The method is applied through first order and represents an extension of the SPT method to excited states. Our method of determining the partition function and various thermodynamic quantities is accurate and efficient and has the potential to yield interesting insight into the role played by the Pauli

  15. Raman spectroscopic signature of fractionalized excitations in the harmonic-honeycomb iridates β- and γ-Li2IrO3

    PubMed Central

    Glamazda, A.; Lemmens, P.; Do, S. -H.; Choi, Y. S.; Choi, K. -Y.

    2016-01-01

    The fractionalization of elementary excitations in quantum spin systems is a central theme in current condensed matter physics. The Kitaev honeycomb spin model provides a prominent example of exotic fractionalized quasiparticles, composed of itinerant Majorana fermions and gapped gauge fluxes. However, identification of the Majorana fermions in a three-dimensional honeycomb lattice remains elusive. Here we report spectroscopic signatures of fractional excitations in the harmonic-honeycomb iridates β- and γ-Li2IrO3. Using polarization-resolved Raman spectroscopy, we find that the dynamical Raman response of β- and γ-Li2IrO3 features a broad scattering continuum with distinct polarization and composition dependence. The temperature dependence of the Raman spectral weight is dominated by the thermal damping of fermionic excitations. These results suggest the emergence of Majorana fermions from spin fractionalization in a three-dimensional Kitaev–Heisenberg system. PMID:27457278

  16. Non-perturbative renormalisation of left left four-fermion operators with Neuberger fermions

    NASA Astrophysics Data System (ADS)

    Dimopoulos, P.; Giusti, L.; Hernández, P.; Palombi, F.; Pena, C.; Vladikas, A.; Wennekers, J.; Wittig, H.

    2006-09-01

    We outline a general strategy for the non-perturbative renormalisation of composite operators in discretisations based on Neuberger fermions, via a matching to results obtained with Wilson-type fermions. As an application, we consider the renormalisation of the four-quark operators entering the ΔS = 1 and ΔS = 2 effective Hamiltonians. Our results are an essential ingredient for the determination of the low-energy constants governing non-leptonic kaon decays.

  17. Odd frequency pairing of interacting Majorana fermions

    NASA Astrophysics Data System (ADS)

    Huang, Zhoushen; Woelfle, Peter; Balatsky, Alexandar

    Majorana fermions are rising as a promising key component in quantum computation. While the prevalent approach is to use a quadratic (i.e. non-interacting) Majorana Hamiltonian, when expressed in terms of Dirac fermions, generically the Hamiltonian involves interaction terms. Here we focus on the possible pair correlations in a simple model system. We study a model of Majorana fermions coupled to a boson mode and show that the anomalous correlator between different Majorana fermions, located at opposite ends of a topological wire, exhibits odd frequency behavior. It is stabilized when the coupling strength g is above a critical value gc. We use both, conventional diagrammatic theory and a functional integral approach, to derive the gap equation, the critical temperature, the gap function, the critical coupling, and a Ginzburg-Landau theory allowing to discuss a possible subleading admixture of even-frequency pairing. Work supported by USDOE DE-AC52-06NA25396 E304, Knut and Alice Wallenberg Foundation, and ERC DM-321031.

  18. Axial gravity, massless fermions and trace anomalies

    NASA Astrophysics Data System (ADS)

    Bonora, L.; Cvitan, M.; Prester, P. Dominis; Pereira, A. Duarte; Giaccari, S.; Štemberga, T.

    2017-08-01

    This article deals with two main topics. One is odd parity trace anomalies in Weyl fermion theories in a 4d curved background, the second is the introduction of axial gravity. The motivation for reconsidering the former is to clarify the theoretical background underlying the approach and complete the calculation of the anomaly. The reference is in particular to the difference between Weyl and massless Majorana fermions and to the possible contributions from tadpole and seagull terms in the Feynman diagram approach. A first, basic, result of this paper is that a more thorough treatment, taking account of such additional terms and using dimensional regularization, confirms the earlier result. The introduction of an axial symmetric tensor besides the usual gravitational metric is instrumental to a different derivation of the same result using Dirac fermions, which are coupled not only to the usual metric but also to the additional axial tensor. The action of Majorana and Weyl fermions can be obtained in two different limits of such a general configuration. The results obtained in this way confirm the previously obtained ones.

  19. Finite volume renormalization scheme for fermionic operators

    SciTech Connect

    Monahan, Christopher; Orginos, Kostas

    2013-11-01

    We propose a new finite volume renormalization scheme. Our scheme is based on the Gradient Flow applied to both fermion and gauge fields and, much like the Schr\\"odinger functional method, allows for a nonperturbative determination of the scale dependence of operators using a step-scaling approach. We give some preliminary results for the pseudo-scalar density in the quenched approximation.

  20. Partial dynamical symmetry in a fermion system

    PubMed

    Escher; Leviatan

    2000-02-28

    The relevance of the partial dynamical symmetry concept for an interacting fermion system is demonstrated. Hamiltonians with partial SU(3) symmetry are presented in the framework of the symplectic shell model of nuclei and shown to be closely related to the quadrupole-quadrupole interaction. Implications are discussed for the deformed light nucleus 20Ne.

  1. Observation of Weyl fermions in condensed matter

    NASA Astrophysics Data System (ADS)

    Ding, Hong

    In 1929, a German mathematician and physicist Hermann Weyl proposed that a massless solution of the Dirac equation represents a pair of new type of particles, the so-called Weyl fermions. However, their existence in particle physics remains elusive after more than eight decades, e.g., neutrino has been regarded as a Weyl fermion in the Standard Model until it was found to have mass. Recently, significant advances in topological materials have provided an alternative way to realize Weyl fermions in condensed matter as an emergent phenomenon. Weyl semimetals are predicted as a class of topological materials that can be regarded as three-dimensional analogs of graphene breaking time reversal or inversion symmetry. Electrons in a Weyl semimetal behave exactly as Weyl fermions, which have many exotic properties, such as chiral anomaly, magnetic monopoles in the crystal momentum space, and open Fermi arcs on the surface. In this talk I will report our experimental discovery of a Weyl semimetal in TaAs by observing Fermi arcs with a characteristic spin texture in the surface states and Weyl nodes in the bulk states using angle-resolved photoemission spectroscopy.

  2. Unorthodox lattice fermion derivatives and their shortcomings

    SciTech Connect

    Bodwin, G.T.; Kovacs, E.V.

    1987-03-10

    We discuss the DWY (Lagrangian), Quinn-Weinstein, and Rebbi proposals for incorporating fermions into lattice gauge theory and analyze them in the context of weak coupling perturbation theory. We find that none of these proposals leads to a completely satisfactory lattice transcription of fully-interacting gauge theory.

  3. On the decoupling of mirror fermions

    NASA Astrophysics Data System (ADS)

    Chen, Chen; Giedt, Joel; Poppitz, Erich

    2013-04-01

    An approach to the formulation of chiral gauge theories on the lattice is to start with a vector-like theory, but decouple one chirality (the "mirror" fermions) using strong Yukawa interactions with a chirally coupled "Higgs" field. While this is an attractive idea, its viability needs to be tested with nonperturbative studies. The model that we study here, the so-called "3-4-5" model, is anomaly free and the presence of massless states in the mirror sector is not required by anomaly matching arguments, in contrast to the "1-0" model that was studied previously. We have computed the polarization tensor in this theory and find a directional discontinuity that appears to be nonzero in the limit of an infinite lattice, which is equivalent to the continuum limit at fixed physical volume. We show that a similar behavior occurs for the free massless Ginsparg-Wilson fermion, where the polarization tensor is known to have a directional discontinuity in the continuum limit. We thus find support for the conclusion that in the continuum limit of the 3-4-5 model, there are massless charged modes in the mirror sector so that it does not decouple from the light sector. The value of the discontinuity we obtain allows for two interpretations: either a chiral gauge theory does not emerge and mirror-sector fermions in a chiral anomaly free representation remain massless, or a massless vectorlike mirror fermion appears. We end by discussing some questions for future study.

  4. Entanglement of several blocks in fermionic chains

    NASA Astrophysics Data System (ADS)

    Ares, Filiberto; Esteve, José G.; Falceto, Fernando

    2014-12-01

    In this paper we propose an expression for the entanglement entropy of several intervals in a stationary state of a free, translational invariant Hamiltonian in a fermionic chain. We check numerically the accuracy of our proposal and conjecture a formula for the asymptotic behavior of principal submatrices of a Toeplitz matrix.

  5. Fermionic entanglement ambiguity in noninertial frames

    SciTech Connect

    Montero, Miguel; Martin-Martinez, Eduardo

    2011-06-15

    We analyze an ambiguity in previous works on entanglement of fermionic fields in noninertial frames. This ambiguity, related to the anticommutation properties of field operators, leads to nonunique results when computing entanglement measures for the same state. We show that the ambiguity disappears when we introduce detectors, which are in any case necessary as a means to probe the field entanglement.

  6. Quantization of gravitation with Weyl fermions

    SciTech Connect

    Schaposnik, F.A.; Vucetich, H.

    1987-12-01

    It is shown that quantization of gravitation consistent with the presence of Weyl fermions is possible, in spite of the existence of Lorentz anomalies; the group of local Lorentz transformations is quantized becoming a physical field and the anomaly is absorbed.

  7. Precision constraints on extra fermion generations.

    PubMed

    Erler, Jens; Langacker, Paul

    2010-07-16

    There has been recent renewed interest in the possibility of additional fermion generations. At the same time there have been significant changes in the relevant electroweak precision constraints, in particular, in the interpretation of several of the low energy experiments. We summarize the various motivations for extra families and analyze them in view of the latest electroweak precision data.

  8. Fermions Living in a Flat World

    SciTech Connect

    Jesus Anguiano-Galicia, Ma. de; Bashir, A.

    2006-09-25

    In a plane, parity transformation, which changes the sign of only one spatial coordinate, swaps the fermion fields living in two inequivalent representations. A parity invariant Lagrangian thus contains fields corresponding to both the representations. For such a Lagrangian, we show that we can also define a chiral symmetry.

  9. Kondo lattice and antiferromagnetic behavior in quaternary CeTAl4Si2 (T = Rh, Ir) single crystals

    SciTech Connect

    Maurya, Arvind; Kulkarni, Ruta; Thamizhavel, Arumugam; Paudyal, Durga; Dhar, Sudesh Kumar

    2016-02-26

    Here, we have explored in detail the anisotropic magnetic properties of CeRhAl4Si2 and CeIrAl4Si2, which undergo two antiferromagnetic transitions, at TN1 = 12.6 and 15.5 K, followed by a second transition at TN2 = 9.4 and 13.8 K, respectively, with the [001]-axis as the relatively easy axis of magnetization. The electrical resistivity at ambient and applied pressure provides evidence of Kondo interaction in both compounds, further supported by a reduced value of the entropy associated with the magnetic ordering. The Sommerfeld coefficient γ is inferred to be 195.6 and 49.4 mJ/(mol K2) for CeRhAl4Si2 and CeIrAl4Si2, respectively, classifying these materials as moderate heavy-fermion compounds. The crystal electric field energy levels are derived from the peak seen in the Schottky heat capacity. Furthermore, we have also performed electronic structure calculations by using the local spin density approximation + U [LSDA+U] approach, which provide physical insights on the observed magnetic behavior of these two compounds.

  10. Ghost free systems with coexisting bosons and fermions

    NASA Astrophysics Data System (ADS)

    Kimura, Rampei; Sakakihara, Yuki; Yamaguchi, Masahide

    2017-08-01

    We study the coexistence system of both bosonic and fermionic degrees of freedom. Even if a Lagrangian does not include higher derivatives, fermionic ghosts exist. For a Lagrangian with up to first derivatives, we find the fermionic ghost free condition in Hamiltonian analysis, which is found to be the same as requiring that the equations of motion of fermions be first order in Lagrangian formulation. When fermionic degrees of freedom are present, the uniqueness of time evolution is not guaranteed a priori because of the Grassmann property. We confirm that the additional condition, which is introduced to close Hamiltonian analysis, also ensures the uniqueness of the time evolution of the system.

  11. Effect of Fermion Velocity on Phase Structure of QED3

    NASA Astrophysics Data System (ADS)

    Li, Jian-Feng; Feng, Hong-Tao; Zong, Hong-Shi

    2016-11-01

    Dynamical chiral symmetry breaking (DCSB) in thermal QED3 with fermion velocity is studied in the framework of Dyson-Schwinger equations. By adopting instantaneous approximation and neglecting the transverse component of gauge boson propagator at finite temperature, we numerically solve the fermion self-energy equation in the rainbow approximation. It is found that both DCSB and fermion chiral condensate are suppressed by fermion velocity. Moreover, the critical temperature decreases as fermion velocity increases. Supported in part by the National Natural Science Foundation of China under Grant No. 11535005 and the Natural Science Foundation of Jiangsu Province under Grant No. BK20130387

  12. Fermions in hybrid loop quantum cosmology

    NASA Astrophysics Data System (ADS)

    Elizaga Navascués, Beatriz; Mena Marugán, Guillermo A.; Martín-Benito, Mercedes

    2017-08-01

    This work pioneers the quantization of primordial fermion perturbations in hybrid loop quantum cosmology (LQC). We consider a Dirac field coupled to a spatially flat, homogeneous, and isotropic cosmology, sourced by a scalar inflaton, and treat the Dirac field as a perturbation. We describe the inhomogeneities of this field in terms of creation and annihilation variables, chosen to admit a unitary evolution if the Dirac fermion were treated as a test field. Considering instead the full system, we truncate its action at quadratic perturbative order and construct a canonical formulation. In particular this implies that, in the global Hamiltonian constraint of the model, the contribution of the homogeneous sector is corrected with a quadratic perturbative term. We then adopt the hybrid LQC approach to quantize the full model, combining the loop representation of the homogeneous geometry with the Fock quantization of the inhomogeneities. We assume a Born-Oppenheimer ansatz for physical states and show how to obtain a Schrödinger equation for the quantum evolution of the perturbations, where the role of time is played by the homogeneous inflaton. We prove that the resulting quantum evolution of the Dirac field is indeed unitary, despite the fact that the underlying homogeneous geometry has been quantized as well. Remarkably, in such evolution, the fermion field couples to an infinite sequence of quantum moments of the homogeneous geometry. Moreover, the evolved Fock vacuum of our fermion perturbations is shown to be an exact solution of the Schrödinger equation. Finally, we discuss in detail the quantum backreaction that the fermion field introduces in the global Hamiltonian constraint. For completeness, our quantum study includes since the beginning (gauge-invariant) scalar and tensor perturbations, that were studied in previous works.

  13. Fermionic-mode entanglement in non-Markovian environment

    SciTech Connect

    Cheng, Jiong; Han, Yan; An, Qing-zhi; Zhou, Ling

    2015-03-15

    We evaluate the non-Markovian effects on the entanglement dynamics of a fermionic system interacting with two dissipative vacuum reservoirs. The exact solution of density matrix is derived by utilizing the Feynman–Vernon influence functional theory in the fermionic coherent state representation and the Grassmann calculus, which are valid for both the fermionic and bosonic baths, and their difference lies in the dependence of the parity of the initial states. The fermionic entanglement dynamics is presented by adding an additional restriction to the density matrix known as the superselection rules. Our analysis shows that the usual decoherence suppression schemes implemented in qubits systems can also be achieved for systems of identical fermions, and the initial state proves its importance in the evolution of fermionic entanglement. Our results provide a potential way to decoherence controlling of identical fermions.

  14. IOT Overview: IR Instruments

    NASA Astrophysics Data System (ADS)

    Mason, E.

    In this instrument review chapter the calibration plans of ESO IR instruments are presented and briefly reviewed focusing, in particular, on the case of ISAAC, which has been the first IR instrument at VLT and whose calibration plan served as prototype for the coming instruments.

  15. IR Hot Wave

    SciTech Connect

    Graham, T. B.

    2010-04-01

    The IR Hot Wave{trademark} furnace is a breakthrough heat treatment system for manufacturing metal components. Near-infrared (IR) radiant energy combines with IR convective heating for heat treating. Heat treatment is an essential process in the manufacture of most components. The controlled heating and cooling of a metal or metal alloy alters its physical, mechanical, and sometimes chemical properties without changing the object's shape. The IR Hot Wave{trademark} furnace offers the simplest, quickest, most efficient, and cost-effective heat treatment option for metals and metal alloys. Compared with other heat treatment alternatives, the IR Hot Wave{trademark} system: (1) is 3 to 15 times faster; (2) is 2 to 3 times more energy efficient; (3) is 20% to 50% more cost-effective; (4) has a {+-}1 C thermal profile compared to a {+-}10 C thermal profile for conventional gas furnaces; and (5) has a 25% to 50% smaller footprint.

  16. Decay of a Yukawa fermion at finite temperature and applications to leptogenesis

    SciTech Connect

    Kiessig, Clemens P.; Pluemacher, Michael; Thoma, Markus H.

    2010-08-01

    We calculate the decay rate of a Yukawa fermion in a thermal bath using finite-temperature cutting rules and effective Green's functions according to the hard thermal loop resummation technique. We apply this result to the decay of a heavy Majorana neutrino in leptogenesis. Compared to the usual approach where thermal masses are inserted into the kinematics of final states, we find that deviations arise through two different leptonic dispersion relations. The decay rate differs from the usual approach by more than 1 order of magnitude in the temperature range which is interesting for the weak washout regime. We discuss how to arrive at consistent finite-temperature treatments of leptogenesis.

  17. Fermion mass hierarchy and nonhierarchical mass ratios in SU(5)xU(1){sub F}

    SciTech Connect

    Duque, Luis F.; Gutierrez, Diego A.; Nardi, Enrico; Norena, Jorge

    2008-08-01

    We consider a SU(5)xU(1){sub F} grand unified theory (GUT)-flavor model in which the number of effects that determine the charged fermions Yukawa matrices is much larger than the number of observables, resulting in a hierarchical fermion spectrum with no particular regularities. The GUT-flavor symmetry is broken by flavons in the adjoint of SU(5), realizing a variant of the Froggatt-Nielsen mechanism that gives rise to a large number of effective operators. By assuming a common mass for the heavy fields and universality of the fundamental Yukawa couplings, we reduce the number of free parameters to one. The observed fermion mass spectrum is reproduced thanks to selection rules that discriminate among various contributions. Bottom-tau Yukawa unification is preserved at leading order, but there is no unification for the first two families. Interestingly, U(1){sub F} charges alone do not determine the hierarchy, and can only give upper bounds on the parametric suppression of the Yukawa operators.

  18. Trace anomaly for non-relativistic fermions

    NASA Astrophysics Data System (ADS)

    Auzzi, Roberto; Baiguera, Stefano; Nardelli, Giuseppe

    2017-08-01

    We study the coupling of a 2 + 1 dimensional non-relativistic spin 1/2 fermion to a curved Newton-Cartan geometry, using null reduction from an extra-dimensional relativistic Dirac action in curved spacetime. We analyze Weyl invariance in detail: we show that at the classical level it is preserved in an arbitrary curved background, whereas at the quantum level it is broken by anomalies. We compute the trace anomaly using the Heat Kernel method and we show that the anomaly coefficients a, c are proportional to the relativistic ones for a Dirac fermion in 3 + 1 dimensions. As for the previously studied scalar case, these coefficents are proportional to 1/ m, where m is the non-relativistic mass of the particle.

  19. Fermionic sound in Bose-Fermi mixtures

    NASA Astrophysics Data System (ADS)

    Gromov, Andrey; Bradlyn, Barry

    2014-03-01

    Sound waves emerge as a result of spontaneously broken symmetry- translational in the case of solids and normal fluids and U(1) phase symmetry in the case of superfluids. Collective modes like these, which result from the breaking of conventional symmetries, usually have bosonic statistics. We explore the consequences of a subtle fermionic symmetry that appears in Bose-Fermi mixtures when both species have equal mass. In particular, we predict the existence of a novel fermionic collective excitation and comment on its properties. We show that this mode persists in the presence of a trapping potential and contact interaction. We describe the fate of these excitations when there is a small mass difference between the two particle species. Lastly, we discuss the possibility of observing this mode in experiments, for example in trapped 174 Yb-173 Yb Bose-Fermi mixtures.

  20. Chiral Scars in Chaotic Dirac Fermion Systems

    NASA Astrophysics Data System (ADS)

    Xu, Hongya; Huang, Liang; Lai, Ying-Cheng; Grebogi, Celso

    2013-02-01

    Do relativistic quantum scars in classically chaotic systems possess unique features that are not shared by nonrelativistic quantum scars? We report a class of relativistic quantum scars in massless Dirac fermion systems whose phases return to the original values or acquire a 2π change only after circulating twice about some classical unstable periodic orbits. We name such scars chiral scars, the successful identification of which has been facilitated tremendously by our development of an analytic, conformal-mapping-based method to calculate an unprecedentedly large number of eigenstates with high accuracy. Our semiclassical theory indicates that the physical origin of chiral scars can be attributed to a combined effect of chirality intrinsic to massless Dirac fermions and the geometry of the underlying classical orbit.