NASA Astrophysics Data System (ADS)
O'Neal, K. R.; Zhou, J.; Cherian, J. G.; Turnbull, M. M.; Landee, C. P.; Jena, P.; Liu, Z.; Musfeldt, J. L.
2016-03-01
We combined synchrotron-based infrared and Raman spectroscopies, diamond anvil cell techniques, and first principles calculations to unveil pressure-induced distortions in quasi-one-dimensional Cu(pyz)(NO3)2. The crossover at 0.7 GPa is local in nature whereas the transition at 5 GPa lowers symmetry from P m n a to P 2221 and is predicted to slightly increase magnetic dimensionality. Comparison with prior magnetoinfrared results reveals the striking role of out-of-plane bending of the pyrazine ligand, a finding that we discuss in terms of the possibility of using pressure to bias the magnetic quantum critical transition in this classic S =1 /2 antiferromagnet.
NASA Astrophysics Data System (ADS)
Kurita, Nobuyuki; Tanaka, Hidekazu
2016-09-01
We have performed magnetization measurements of the gapped quantum magnet CsFeCl3 at temperatures (T ) down to 0.5 K at ambient pressure and down to 1.8 K at hydrostatic pressures (P ) of up to 1.5 GPa. The lower-field (H ) phase boundary of the field-induced ordered phase at ambient pressure is found to follow the power-law behavior expressed by the formula HN(T ) -Hc∝TNϕ . The application of pressure extends the phase boundary to both a lower field and higher temperature. Above the critical pressure Pc˜0.9 GPa, the transition field HN associated with the excitation gap becomes zero, and a signature of the magnetic phase transition is found in the T dependence of magnetization in a very low applied field. This suggests that CsFeCl3 exhibits a pressure-induced magnetic phase transition at Pc.
Magnetic-field- and pressure-induced quantum phases in complex materials.
Kim, Minjung; Barath, Harini; Chen, Xiaoqian; Joe, Young-Il; Fradkin, Eduardo; Abbamonte, Peter; Cooper, S Lance
2010-03-12
This Progress Report presents temperature-, magnetic-field-, and pressure-dependent Raman measurements of strongly correlated materials such as the charge-ordering manganese perovskites, the multiferroic material TbMnO(3), and the charge-density wave (CDW) materials 1T-TiSe(2) and Cu(x)TiSe(2). These studies illustrate the rich array of phases and properties that can be accessed with field and pressure tuning in these materials, and demonstrate the efficacy of using magnetic-field- and pressure-dependent scattering methods to elucidate the microscopic changes associated with highly tunable behavior in complex materials. PMID:20401939
Pressure-induced magnetic instability in Pd-Ni alloys
NASA Astrophysics Data System (ADS)
Oomi, Gendo; Iwai, Sadanori; Ohashi, Masashi; Nakano, Tomohito
2012-12-01
The electrical resistivity ρ(T) of dilute Pd-Ni alloys has been measured at high pressure up to 3 GPa. It is found that the ρ(T) of the ferromagnetic Pd-Ni alloy shows an anomalous temperature dependence near the critical pressure Pc, where the ferromagnetism disappears. The results are analysed in the framework of quantum critical behaviour induced by pressure. The effect of magnetic field on the ρ(T) is also examined. Different behaviour of magnetoresistance against pressure was found depending on the alloy concentration and discussed in connection with an instability of ferromagnetism.
Field-induced quantum critical point in the pressure-induced superconductor CeRhIn5
Bauer, Eric D; Park, Tuson; Tokiwa, Yoshifumi; Ronning, Filip; Lee, Han O; Movshovich, Roman; Thompson, Joe D
2009-01-01
When subjected to pressure, the prototypical heavy-fermion antiferromagnet CeRhIn{sub 5} becomes superconducting, forming a broad dome of superconductivity centered around 2.35 GPa (=P2) with maximal T{sub c} of 2.3 K. Above the superconducting dome, the normal state shows strange metallic behaviors, including a divergence in the specific heat and a sub-T-linear electrical resistivity. The discovery of a field-induced magnetic phase that coexists with superconductivity for a range of pressures P {le} P2 has been interpreted as evidence for a quantum phase transition, which could explain the non-Fenni liquid behavior observed in the normal state. Here we report electrical resistivity measurements of CeRhIn{sub 5} under magnetic field at P2, where the resistivity is sub-T-linear for fields less than H{sub c2}(0) and a T{sup 2}-coefficient A found above H{sub c2}(0) diverges as H{sub c2} is approached. These results are similar to the field-induced quantum critical compound Ce-CoIn{sub 5} and confirm the presence of a quantum critical point in the pressure-induced superconductor CeRhIn{sub 5}.
Quantum Oscillation Signatures of Pressure-induced Topological Phase Transition in BiTeI
Park, Joonbum; Jin, Kyung-Hwan; Jo, Y. J.; Choi, E. S.; Kang, W.; Kampert, E.; Rhyee, J.-S.; Jhi, Seung-Hoon; Kim, Jun Sung
2015-01-01
We report the pressure-induced topological quantum phase transition of BiTeI single crystals using Shubnikov-de Haas oscillations of bulk Fermi surfaces. The sizes of the inner and the outer FSs of the Rashba-split bands exhibit opposite pressure dependence up to P = 3.35 GPa, indicating pressure-tunable Rashba effect. Above a critical pressure P ~ 2 GPa, the Shubnikov-de Haas frequency for the inner Fermi surface increases unusually with pressure, and the Shubnikov-de Haas oscillations for the outer Fermi surface shows an abrupt phase shift. In comparison with band structure calculations, we find that these unusual behaviors originate from the Fermi surface shape change due to pressure-induced band inversion. These results clearly demonstrate that the topological quantum phase transition is intimately tied to the shape of bulk Fermi surfaces enclosing the time-reversal invariant momenta with band inversion. PMID:26522628
Pressure induced superconductivity on the border of magnetic order in MnP.
Cheng, J-G; Matsubayashi, K; Wu, W; Sun, J P; Lin, F K; Luo, J L; Uwatoko, Y
2015-03-20
We report the discovery of superconductivity on the border of long-range magnetic order in the itinerant-electron helimagnet MnP via the application of high pressure. Superconductivity with T(sc)≈1 K emerges and exists merely near the critical pressure P(c)≈8 GPa, where the long-range magnetic order just vanishes. The present finding makes MnP the first Mn-based superconductor. The close proximity of superconductivity to a magnetic instability suggests an unconventional pairing mechanism. Moreover, the detailed analysis of the normal-state transport properties evidenced non-Fermi-liquid behavior and the dramatic enhancement of the quasiparticle effective mass near P(c) associated with the magnetic quantum fluctuations.
Magnetic Precursor of the Pressure-Induced Superconductivity in Fe-Ladder Compounds
NASA Astrophysics Data System (ADS)
Chi, Songxue; Uwatoko, Yoshiya; Cao, Huibo; Hirata, Yasuyuki; Hashizume, Kazuki; Aoyama, Takuya; Ohgushi, Kenya
2016-07-01
The pressure effects on the antiferromagentic orders in iron-based ladder compounds CsFe2Se3 and BaFe2S3 have been studied using neutron diffraction. With identical crystal structure and similar magnetic structures, the two compounds exhibit highly contrasting magnetic behaviors under moderate external pressures. In CsFe2Se3 the ladders are brought much closer to each other by pressure, but the stripe-type magnetic order shows no observable change. In contrast, the stripe order in BaFe2S3 undergoes a quantum phase transition where an abrupt increase of Néel temperature by more than 50% occurs at about 1 GPa, accompanied by a jump in the ordered moment. With its spin structure unchanged, BaFe2S3 enters an enhanced magnetic phase that bears the characteristics of an orbital selective Mott phase, which is the true neighbor of superconductivity emerging at higher pressures.
Magnetic Precursor of the Pressure-Induced Superconductivity in Fe-Ladder Compounds
Chi, Songxue; Uwatoko, Yoshiya; Cao, Huibo; Hirata, Yasuyuki; Hashizume, Kazuki; Aoyama, Takuya; Ohgushi, Kenya
2016-07-21
We studied the pressure effects on the antiferromagentic orders in iron-based ladder compounds CsFemore » $_2$Se$_3$ and BaFe$_2$S$_3$ using single crytal neutron diffraction technique. With identical crystal structure and similar magnetic structures, the two compounds exhibit highly contrasting magnetic behaviors under moderate external pressures. In CsFe$_2$Se$_3$ the ladders are brought much closer to each other by pressure, but the stripe-type of magnetic order shows no observable change. Furthermore, the stripe order in BaFe$_2$S$_3$, undergoes a quantum phase transition where an abrupt increase of $$N\\acute{e}el$$ temperature by more than 50$$\\%$$ occurs at about 1 GPa, accompanied by a jump in ordered moment. Finally, with its spin structure unchanged, BaFe$_2$S$_3$ enters an enhanced magnetic phase that bears the characteristics of an orbital selective Mott phase, which is the true herald for superconductivity emerging at higher pressures.« less
Spiral magnetic order and pressure-induced superconductivity in transition metal compounds
Wang, Yishu; Feng, Yejun; Cheng, J.-G.; Wu, W.; Luo, J. L.; Rosenbaum, T. F.
2016-01-01
Magnetic and superconducting ground states can compete, cooperate and coexist. MnP provides a compelling and potentially generalizable example of a material where superconductivity and magnetism may be intertwined. Using a synchrotron-based non-resonant X-ray magnetic diffraction technique, we reveal a spiral spin order in MnP and trace its pressure evolution towards superconducting order via measurements in a diamond anvil cell. Judging from the magnetostriction, ordered moments vanish at the quantum phase transition as pressure increases the electron kinetic energy. Spins remain local in the disordered phase, and the promotion of superconductivity is likely to emerge from an enhanced coupling to residual spiral spin fluctuations and their concomitant suppression of phonon-mediated superconductivity. As the pitch of the spiral order varies across the 3d transition metal compounds in the MnP family, the magnetic ground state switches between antiferromagnet and ferromagnet, providing an additional tuning parameter in probing spin-fluctuation-induced superconductivity. PMID:27708255
Spiral magnetic order and pressure-induced superconductivity in transition metal compounds
NASA Astrophysics Data System (ADS)
Wang, Yishu; Feng, Yejun; Cheng, J.-G.; Wu, W.; Luo, J. L.; Rosenbaum, T. F.
2016-10-01
Magnetic and superconducting ground states can compete, cooperate and coexist. MnP provides a compelling and potentially generalizable example of a material where superconductivity and magnetism may be intertwined. Using a synchrotron-based non-resonant X-ray magnetic diffraction technique, we reveal a spiral spin order in MnP and trace its pressure evolution towards superconducting order via measurements in a diamond anvil cell. Judging from the magnetostriction, ordered moments vanish at the quantum phase transition as pressure increases the electron kinetic energy. Spins remain local in the disordered phase, and the promotion of superconductivity is likely to emerge from an enhanced coupling to residual spiral spin fluctuations and their concomitant suppression of phonon-mediated superconductivity. As the pitch of the spiral order varies across the 3d transition metal compounds in the MnP family, the magnetic ground state switches between antiferromagnet and ferromagnet, providing an additional tuning parameter in probing spin-fluctuation-induced superconductivity.
Magnetic Precursor of the Pressure-Induced Superconductivity in Fe-Ladder Compounds.
Chi, Songxue; Uwatoko, Yoshiya; Cao, Huibo; Hirata, Yasuyuki; Hashizume, Kazuki; Aoyama, Takuya; Ohgushi, Kenya
2016-07-22
The pressure effects on the antiferromagentic orders in iron-based ladder compounds CsFe_{2}Se_{3} and BaFe_{2}S_{3} have been studied using neutron diffraction. With identical crystal structure and similar magnetic structures, the two compounds exhibit highly contrasting magnetic behaviors under moderate external pressures. In CsFe_{2}Se_{3} the ladders are brought much closer to each other by pressure, but the stripe-type magnetic order shows no observable change. In contrast, the stripe order in BaFe_{2}S_{3} undergoes a quantum phase transition where an abrupt increase of Néel temperature by more than 50% occurs at about 1 GPa, accompanied by a jump in the ordered moment. With its spin structure unchanged, BaFe_{2}S_{3} enters an enhanced magnetic phase that bears the characteristics of an orbital selective Mott phase, which is the true neighbor of superconductivity emerging at higher pressures. PMID:27494496
NASA Astrophysics Data System (ADS)
Gilder, S. A.; Egli, R.; Hochleitner, R.; Roud, S. C.; Volk, M.; Le Goff, M.; de Wit, M.
2010-12-01
Meteorites and diamonds encounter high-pressures during their geologic histories. These materials commonly contain magnetic inclusions of pyrrhotite, and because magnetic properties are sensitive to strain, pyrrhotite can potentially record the shock or formation pressures of its host. Moreover, pyrrhotite undergoes a pressure-induced phase transition between 1.6 and 6.2 GPa, but the magnetic signature of this transition is poorly known. Here we report magnetic measurements performed at high-pressures on single and multi-domain pyrrhotite. A magnetic hysteresis model based on our observations suggests that multidomain pyrrhotite transforms into single domain-like material, and once in the single domain state, hysteresis loops become progressively squarer and then squatter with increasing pressure, until they ultimately collapse approaching the paramagnetic state at the transition. The ratio of the bulk magnetic coercive force to magnetic remanence for pure pyrrhotite is reversible with pressure and follows a logarithmic law as a function of pressure, which can be used as a magnetic barometer for natural systems.
NASA Astrophysics Data System (ADS)
Shen, Yao; Wang, Qisi; Hao, Yiqing; Pan, Bingying; Feng, Yu; Huang, Qingzhen; Harriger, L. W.; Leao, J. B.; Zhao, Yang; Chisnell, R. M.; Lynn, J. W.; Cao, Huibo; Hu, Jiangping; Zhao, Jun
2016-02-01
We use neutron diffraction to study the structure and magnetic phase diagram of the newly discovered pressure-induced superconductor CrAs. Unlike most magnetic unconventional superconductors where the magnetic moment direction barely changes upon doping, here we show that CrAs exhibits a spin reorientation from the a b plane to the a c plane, along with an abrupt drop of the magnetic propagation vector at a critical pressure (Pc≈0.6 GPa). This magnetic phase transition, accompanied by a lattice anomaly, coincides with the emergence of bulk superconductivity. With further increasing pressure, the magnetic order completely disappears near the optimal Tc regime (P ≈0.94 GPa). Moreover, the Cr magnetic moments tend to be aligned antiparallel between nearest neighbors with increasing pressure toward the optimal superconductivity regime. Our findings suggest that the noncollinear helimagnetic order is strongly coupled to structural and electronic degrees of freedom, and that the antiferromagnetic correlations between nearest neighbors might be essential for superconductivity.
NASA Astrophysics Data System (ADS)
Vignesh, G.; Nithiananthi, P.
2016-04-01
The influence of pressure along the growth axis on carrier localization in GaAs/Al0.3Ga0.7As Double Quantum Well (DQW) is studied under strongly coupled regime and isolated regimes of the well. The effective mass approximation combined with variation technique is adopted with the inclusion of mismatches in effective mass and dielectric constants of the well and barrier material. Effect of the barrier and well on carrier localization is investigated by observing the diamagnetic susceptibility (χdia) for various impurity locations (zi) and the critical limit of the barrier (Lb ≈ 50 Å) for tunneling has also been estimated. The effect of Γ-Χ crossover due to the application of pressure on the donor localization is picturized through diamagnetic susceptibility.
Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs
Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; Luetkens, Hubertus; Amato, Alex; Biswas, Pabitra K.; Ruegg, Christian; Susner, Michael A.; Sefat, Athena S.; Zhigadlo, Nikolai D.; et al
2015-09-08
We report that the recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreasesmore » upon increasing the pressure. In the intermediate pressure region (3.5≲ p ≲ 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with Tc3.2 as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.« less
Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs.
Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; Luetkens, Hubertus; Amato, Alex; Biswas, Pabitra K; Rüegg, Christian; Susner, Michael A; Sefat, Athena S; Zhigadlo, Nikolai D; Morenzoni, Elvezio
2015-01-01
The recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5 < or ~ p < or ~ 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with Tc(3.2) as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs. PMID:26346548
Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs
Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; Luetkens, Hubertus; Amato, Alex; Biswas, Pabitra K.; Ruegg, Christian; Susner, Michael A.; Sefat, Athena S.; Zhigadlo, Nikolai D.; Morenzoni, Elvezio
2015-09-08
We report that the recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum T_{c} ≃ 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5≲ p ≲ 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (T_{c}) and of the superfluid density (ρ_{s}). A scaling of ρ_{s} with T_{c}^{3.2} as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.
Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs
Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; Luetkens, Hubertus; Amato, Alex; Biswas, Pabitra K.; Rüegg, Christian; Susner, Michael A.; Sefat, Athena S.; Zhigadlo, Nikolai D.; Morenzoni, Elvezio
2015-01-01
The recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5 p 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs. PMID:26346548
Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs.
Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; Luetkens, Hubertus; Amato, Alex; Biswas, Pabitra K; Rüegg, Christian; Susner, Michael A; Sefat, Athena S; Zhigadlo, Nikolai D; Morenzoni, Elvezio
2015-09-08
The recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5 < or ~ p < or ~ 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with Tc(3.2) as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.
Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs
NASA Astrophysics Data System (ADS)
Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; Luetkens, Hubertus; Amato, Alex; Biswas, Pabitra K.; Rüegg, Christian; Susner, Michael A.; Sefat, Athena S.; Zhigadlo, Nikolai D.; Morenzoni, Elvezio
2015-09-01
The recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5 p 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.
Jung, Soon-Gil; Kang, Ji-Hoon; Park, Eunsung; Lee, Sangyun; Lin, Jiunn-Yuan; Chareev, Dmitriy A.; Vasiliev, Alexander N.; Park, Tuson
2015-01-01
We investigate the relation of the critical current density (Jc) and the remarkably increased superconducting transition temperature (Tc) for the FeSe single crystals under pressures up to 2.43 GPa, where the Tc is increased by ~8 K/GPa. The critical current density corresponding to the free flux flow is monotonically enhanced by pressure which is due to the increase in Tc, whereas the depinning critical current density at which the vortex starts to move is more influenced by the pressure-induced magnetic state compared to the increase of Tc. Unlike other high-Tc superconductors, FeSe is not magnetic, but superconducting at ambient pressure. Above a critical pressure where magnetic state is induced and coexists with superconductivity, the depinning Jc abruptly increases even though the increase of the zero-resistivity Tc is negligible, directly indicating that the flux pinning property compared to the Tc enhancement is a more crucial factor for an achievement of a large Jc. In addition, the sharp increase in Jc in the coexisting superconducting phase of FeSe demonstrates that vortices can be effectively trapped by the competing antiferromagnetic order, even though its antagonistic nature against superconductivity is well documented. These results provide new guidance toward technological applications of high-temperature superconductors. PMID:26548444
Jung, Soon-Gil; Kang, Ji-Hoon; Park, Eunsung; Lee, Sangyun; Lin, Jiunn-Yuan; Chareev, Dmitriy A; Vasiliev, Alexander N; Park, Tuson
2015-01-01
We investigate the relation of the critical current density (Jc) and the remarkably increased superconducting transition temperature (Tc) for the FeSe single crystals under pressures up to 2.43 GPa, where the Tc is increased by ~8 K/GPa. The critical current density corresponding to the free flux flow is monotonically enhanced by pressure which is due to the increase in Tc, whereas the depinning critical current density at which the vortex starts to move is more influenced by the pressure-induced magnetic state compared to the increase of Tc. Unlike other high-Tc superconductors, FeSe is not magnetic, but superconducting at ambient pressure. Above a critical pressure where magnetic state is induced and coexists with superconductivity, the depinning Jc abruptly increases even though the increase of the zero-resistivity Tc is negligible, directly indicating that the flux pinning property compared to the Tc enhancement is a more crucial factor for an achievement of a large Jc. In addition, the sharp increase in Jc in the coexisting superconducting phase of FeSe demonstrates that vortices can be effectively trapped by the competing antiferromagnetic order, even though its antagonistic nature against superconductivity is well documented. These results provide new guidance toward technological applications of high-temperature superconductors. PMID:26548444
Pressure-Induced Enhanced Magnetic Anisotropy in Mn(N(CN)2)2
Quintero, P. A.; Rajan, D.; Peprah, M. K.; Brinzari, T. V.; Fishman, Randy Scott; Talham, Daniel R.; Meisel, Mark W.
2015-01-01
Using DC and AC magnetometry, the pressure dependence of the magnetization of the threedimensional antiferromagnetic coordination polymer Mn(N(CN)2)2 was studied up to 12 kbar and down to 8 K. The magnetic transition temperature, Tc, increases dramatically with applied pressure (P), where a change from Tc(P = ambient) = 16:0 K to Tc(P = 12:1 kbar) = 23:5 K was observed. In addition, a marked difference in the magnetic behavior is observed above and below 7.1 kbar. Specifically, for P < 7:1 kbar, the differences between the field-cooled and zero-field-cooled (fc-zfc) magnetizations, the coercive field, and the remanent magnetization decrease with increasing pressure. However, for P > 7:1 kbar, the behavior is inverted. Additionally, for P > 8:6 kbar, minor hysteresis loops are observed. All of these effects are evidence of the increase of the superexchange interaction and the appearance of an enhanced exchange anisotropy with applied pressure.
Strong cooperative coupling of pressure-induced magnetic order and nematicity in FeSe
NASA Astrophysics Data System (ADS)
Kothapalli, K.; Böhmer, A. E.; Jayasekara, W. T.; Ueland, B. G.; Das, P.; Sapkota, A.; Taufour, V.; Xiao, Y.; Alp, E.; Bud'Ko, S. L.; Canfield, P. C.; Kreyssig, A.; Goldman, A. I.
2016-09-01
A hallmark of the iron-based superconductors is the strong coupling between magnetic, structural and electronic degrees of freedom. However, a universal picture of the normal state properties of these compounds has been confounded by recent investigations of FeSe where the nematic (structural) and magnetic transitions appear to be decoupled. Here, using synchrotron-based high-energy x-ray diffraction and time-domain Mössbauer spectroscopy, we show that nematicity and magnetism in FeSe under applied pressure are indeed strongly coupled. Distinct structural and magnetic transitions are observed for pressures between 1.0 and 1.7 GPa and merge into a single first-order transition for pressures >~1.7 GPa, reminiscent of what has been found for the evolution of these transitions in the prototypical system Ba(Fe1-xCox)2As2. Our results are consistent with a spin-driven mechanism for nematic order in FeSe and provide an important step towards a universal description of the normal state properties of the iron-based superconductors.
Strong cooperative coupling of pressure-induced magnetic order and nematicity in FeSe.
Kothapalli, K; Böhmer, A E; Jayasekara, W T; Ueland, B G; Das, P; Sapkota, A; Taufour, V; Xiao, Y; Alp, E; Bud'ko, S L; Canfield, P C; Kreyssig, A; Goldman, A I
2016-01-01
A hallmark of the iron-based superconductors is the strong coupling between magnetic, structural and electronic degrees of freedom. However, a universal picture of the normal state properties of these compounds has been confounded by recent investigations of FeSe where the nematic (structural) and magnetic transitions appear to be decoupled. Here, using synchrotron-based high-energy x-ray diffraction and time-domain Mössbauer spectroscopy, we show that nematicity and magnetism in FeSe under applied pressure are indeed strongly coupled. Distinct structural and magnetic transitions are observed for pressures between 1.0 and 1.7 GPa and merge into a single first-order transition for pressures ≳1.7 GPa, reminiscent of what has been found for the evolution of these transitions in the prototypical system Ba(Fe1-xCox)2As2. Our results are consistent with a spin-driven mechanism for nematic order in FeSe and provide an important step towards a universal description of the normal state properties of the iron-based superconductors. PMID:27582003
Pressure induced magnetic and semiconductor–metal phase transitions in Cr2MoO6
NASA Astrophysics Data System (ADS)
San-Dong, Guo
2016-05-01
We investigate magnetic ordering and electronic structures of Cr2MoO6 under hydrostatic pressure. To overcome the band gap problem, the modified Becke and Johnson exchange potential is used to investigate the electronic structures of Cr2MoO6. The insulating nature at the experimental crystal structure is produced, with a band gap of 1.04 eV, and the magnetic moment of the Cr atom is 2.50 μ B, compared to an experimental value of about 2.47 μ B. The calculated results show that an antiferromagnetic inter-bilayer coupling–ferromagnetic intra-bilayer coupling to a ferromagnetic inter-bilayer coupling–antiferromagnetic intra-bilayer coupling phase transition is produced with the pressure increasing. The magnetic phase transition is simultaneously accompanied by a semiconductor–metal phase transition. The magnetic phase transition can be explained by the Mo–O hybridization strength, and ferromagnetic coupling between two Cr atoms can be understood by empty Mo-d bands perturbing the nearest O-p orbital. Project supported by the Fundamental Research Funds for the Central Universities, China (Grant No. 2015XKMS073).
Strong cooperative coupling of pressure-induced magnetic order and nematicity in FeSe
Kothapalli, K.; Böhmer, A. E.; Jayasekara, W. T.; Ueland, B. G.; Das, P.; Sapkota, A.; Taufour, V.; Xiao, Y.; Alp, E.; Bud'ko, S. L.; Canfield, P. C.; Kreyssig, A.; Goldman, A. I.
2016-01-01
A hallmark of the iron-based superconductors is the strong coupling between magnetic, structural and electronic degrees of freedom. However, a universal picture of the normal state properties of these compounds has been confounded by recent investigations of FeSe where the nematic (structural) and magnetic transitions appear to be decoupled. Here, using synchrotron-based high-energy x-ray diffraction and time-domain Mössbauer spectroscopy, we show that nematicity and magnetism in FeSe under applied pressure are indeed strongly coupled. Distinct structural and magnetic transitions are observed for pressures between 1.0 and 1.7 GPa and merge into a single first-order transition for pressures ≳1.7 GPa, reminiscent of what has been found for the evolution of these transitions in the prototypical system Ba(Fe1−xCox)2As2. Our results are consistent with a spin-driven mechanism for nematic order in FeSe and provide an important step towards a universal description of the normal state properties of the iron-based superconductors. PMID:27582003
Pressure induced magnetic and semiconductor-metal phase transitions in Cr2MoO6
NASA Astrophysics Data System (ADS)
San-Dong, Guo
2016-05-01
We investigate magnetic ordering and electronic structures of Cr2MoO6 under hydrostatic pressure. To overcome the band gap problem, the modified Becke and Johnson exchange potential is used to investigate the electronic structures of Cr2MoO6. The insulating nature at the experimental crystal structure is produced, with a band gap of 1.04 eV, and the magnetic moment of the Cr atom is 2.50 μ B, compared to an experimental value of about 2.47 μ B. The calculated results show that an antiferromagnetic inter-bilayer coupling-ferromagnetic intra-bilayer coupling to a ferromagnetic inter-bilayer coupling-antiferromagnetic intra-bilayer coupling phase transition is produced with the pressure increasing. The magnetic phase transition is simultaneously accompanied by a semiconductor-metal phase transition. The magnetic phase transition can be explained by the Mo-O hybridization strength, and ferromagnetic coupling between two Cr atoms can be understood by empty Mo-d bands perturbing the nearest O-p orbital. Project supported by the Fundamental Research Funds for the Central Universities, China (Grant No. 2015XKMS073).
Structural response in FeCl2 (iron chloride) to pressure-induced electro-magnetic transitions
Taylor, R D; Rozenberg, G Kh; Pasternak, M P; Gorodetsky, P; Xu, W M; Dubrovinsky, L S; Le Bihan, T L
2009-01-01
High pressure (HP) synchrotron x-ray diffraction studies were carried out in FeCl{sub 2} together with resistivity (R) studies, at various temperatures and pressures to 65 GPa using diamond anvil cells. This work follows a previous HP {sup 57}Fe Mossbauer study in which two pressure-induced (PI) electronic transitions were found interpreted as: (i) quenching of the orbital-term contribution to the hyperfine field concurring with a tilting of the magnetic moment by 55 degrees and (ii) collapse of the magnetism concurring with a sharp decrease of the isomer shift (IS). The R(P,T) studies affirm that the cause the collapse of the magnetism is a PI p-d correlation breakdown, leading to an insulator-metal transition at {approx}45 GPa and is not due to a spi-Ir,crossover (S=2 {yields} S=0). The structure response to the pressure evolution of the two electronic phase transitions starting at low pressures (LP), through an intermediate phase (IP) 30-57 GPa, and culminating in a high-pressure phase (HP), P >32 GPa, can clearly be quantified. The IP-HP phases coexist through the 32-57 GPa range in which the HP abundance increases monotonically at the expense of the IP phase. At the LP-IP interface no volume change is detected, yet the c-axis increases and the a-axis shrinks by 0.21 Angstroms and 0.13 Angstroms, respectively. The fit of the equation of state of the combined LP-IP phases yields a bulk modulus K{sub 0} = 35.3(1.8) GPa. The intralayer CI-CI distances increases, but no change is observed in Fe-CI bond-length nor are there substantial changes in the interlayer spacing. The pressure-induced electronic IP-HP transition leads to a first-order structural phase transition characterized by a decrease in Fe-CI bond length and an abrupt drop in V(P) by {approx}3.5% accompanying the correlation breakdown. In this transition no symmetry change is detected,and the XRD data could be satisfactorily fitted with the CdI{sub 2} structure. The bulk modulus of the HP phase is
Pressure-induced magnetic transitions with change of the orbital configuration in dimerised systems
Korotin, Dmitry M.; Anisimov, Vladimir I.; Streltsov, Sergey V.
2016-01-01
We suggest a possible scenario for magnetic transition under pressure in dimerised systems where electrons are localised on molecular orbitals. The mechanism of transition is not related with competition between kinetic energy and on-site Coulomb repulsion as in Mott-Hubbard systems, or between crystal-field splitting and intra-atomic exchange as in classical atomic spin-state transitions. Instead, it is driven by the change of bonding-antibonding splitting on part of the molecular orbitals. In the magnetic systems with few half-filled molecular orbitals external pressure may result in increase of the bonding-antibonding splitting and localise all electrons on low-lying molecular orbitals suppressing net magnetic moment of the system. We give examples of the systems, where this or inverse transition may occur and by means of ab initio band structure calculations predict that it can be observed in α−MoCl4 at pressure P ~ 11 GPa. PMID:27189206
Quantum magnetic deflagration in acetate.
Hernández-Mínguez, A; Hernandez, J M; Macià, F; García-Santiago, A; Tejada, J; Santos, P V
2005-11-18
We report controlled ignition of magnetization reversal avalanches by surface acoustic waves in a single crystal of acetate. Our data show that the speed of the avalanche exhibits maxima on the magnetic field at the tunneling resonances of Mn(12). Combined with the evidence of magnetic deflagration in Mn(12) acetate, this suggests a novel physical phenomenon: deflagration assisted by quantum tunneling. PMID:16384178
Quantum magnetic deflagration in acetate.
Hernández-Mínguez, A; Hernandez, J M; Macià, F; García-Santiago, A; Tejada, J; Santos, P V
2005-11-18
We report controlled ignition of magnetization reversal avalanches by surface acoustic waves in a single crystal of acetate. Our data show that the speed of the avalanche exhibits maxima on the magnetic field at the tunneling resonances of Mn(12). Combined with the evidence of magnetic deflagration in Mn(12) acetate, this suggests a novel physical phenomenon: deflagration assisted by quantum tunneling.
NASA Astrophysics Data System (ADS)
Zou, T.; Cao, H. B.; Liu, G. Q.; Peng, J.; Gottschalk, M.; Zhu, M.; Zhao, Y.; Leão, J. B.; Tian, W.; Mao, Z. Q.; Ke, X.
2016-07-01
We report the hydrostatic pressure-induced electronic and magnetic phase transitions in a Mott insulator, a bilayer ruthenate C a3(Ru0.97Ti0.03 ) 2O7 , via electronic transport and single crystal neutron diffraction measurements. The system undergoes an insulator-metal transition at a very small hydrostatic pressure ≈0.04 GPa, followed by a magnetic phase transition around 0.3 GPa, suggesting that the low energy charge fluctuation and magnetic ordering couple to the pressure separately in this compound. The a b initio calculations show that the suppressed Ru O6 flattening induced by the pressure reduces the orbital polarization and gives rise to an insulator-metal transition preceding the magnetic phase transition.
Magnetically driven quantum heat engine.
Muñoz, Enrique; Peña, Francisco J
2014-05-01
We studied the efficiency of two different schemes for a magnetically driven quantum heat engine, by considering as the "working substance" a single nonrelativistic particle trapped in a cylindrical potential well, in the presence of an external magnetic field. The first scheme is a cycle, composed of two adiabatic and two isoenergetic reversible trajectories in configuration space. The trajectories are driven by a quasistatic modulation of the external magnetic-field intensity. The second scheme is a variant of the former, where the isoenergetic trajectories are replaced by isothermal ones, along which the system is in contact with macroscopic thermostats. This second scheme constitutes a quantum analog of the classical Carnot cycle.
Magnetically driven quantum heat engine
NASA Astrophysics Data System (ADS)
Munoz, Enrique; Pena, Francisco
2015-03-01
In analogy with classical thermodynamics, a quantum heat engine generates useful mechanical work from heat, by means of a reversible sequence of transformations (trajectories), where the ``working substance'' is of quantum mechanical nature. Several theoretical implementations for a quantum heat engine have been discussed in the literature, such as entangled states in a qubit, quantum mechanical versions of the Otto cycle, and photocells. In this work, we propose yet a different alternative by introducing the concept of a magnetically driven quantum heat engine. We studied the efficiency of such system, by considering as the ``working substance'' a single nonrelativistic particle trapped in a cylindrical potential well, as a model for a semiconductor quantum dot, in the presence of an external magnetic field. The trajectories are driven by a quasistatic modulation of the external magnetic-field intensity, while the system is in contact with macroscopic thermostats. The external magnetic field modulation allows to modify the effective geometric confinement, in analogy with a piston in a classical gas. E. Munoz acknowledges financial support from Fondecyt under Contract 1141146.
Filamentation instability in a quantum magnetized plasma
Bret, A.
2008-02-15
The filamentation instability occurring when a nonrelativistic electron beam passes through a quantum magnetized plasma is investigated by means of a cold quantum magnetohydrodynamic model. It is proved that the instability can be completely suppressed by quantum effects if and only if a finite magnetic field is present. A dimensionless parameter is identified that measures the strength of quantum effects. Strong quantum effects allow for a much smaller magnetic field to suppress the instability than in the classical regime.
Pressure-induced interband optical transitions in an InAs0.8P0.2/InP quantum wire
NASA Astrophysics Data System (ADS)
Saravanan, S.; Peter, A. John; Lee, Chang Woo
2015-12-01
Hydrostatic pressure-induced exciton binding energy in an InAs0.8P0.2/InP quantum well wire is investigated taking into account the geometrical confinement effect. Numerical calculations are carried out using variational approach within the single-band effective-mass approximation. The compressive strain contribution to the confinement potential is included throughout the calculations. The energy difference of the ground and the first excited state is found with the consideration of spatial confinement effect in the influence of pressure. The second-order susceptibility of harmonic generation is carried out using the compact density method. The optical gain as a function of incident photon energy is computed in the presence of the hydrostatic pressure. The result shows that the range of wavelength for the potential applications of telecommunications (1.3-1.55 μm) can be obtained by the application of the hydrostatic pressure. We believe that the obtained results can be applied for tuning the ranges of fibre optical wavelength in telecommunications.
Pressure-induced changes in the magnetic and magnetocaloric properties of RMn2Ge2 (R=Sm,Gd)
NASA Astrophysics Data System (ADS)
Kumar, Pramod; Suresh, K. G.; Nigam, A. K.; Magnus, A.; Coelho, A. A.; Gama, S.
2008-06-01
We have studied the variation of magnetic and magnetocaloric properties of polycrystalline compounds SmMn2Ge2 and GdMn2Ge2 as a function of applied hydrostatic pressure. The magnetic transition temperatures are found to change considerably with pressure. The temperature regime of existence of antiferromagnetic (AFM) ordering is found to increase with pressure, in both the compounds. In SmMn2Ge2 , the sign of the magnetocaloric effect at the low-temperature ferromagnetic (FM)-AFM transition changes with pressure. The isothermal magnetic entropy change in this compound is found to increase by about 20 times as the pressure is increased from the ambient value to 6.8 kbar. Effect of pressure in GdMn2Ge2 is less compared to that in SmMn2Ge2 . The variations in the magnetic and magnetocaloric properties are attributed to the changes in the magnetic state of the Mn sublattice under pressure. The difference in R-Mn coupling in Sm and Gd compounds is also found to play a role in determining the magnetic and magnetocaloric properties, both at ambient as well as under applied pressures.
Quantum vacuum magnetic birefringence
NASA Astrophysics Data System (ADS)
Berceau, Paul; Battesti, Rémy; Fouché, Mathilde; Frings, Paul; Nardone, Marc; Portugall, Oliver; Rikken, Geert L. J. A.; Rizzo, Carlo
2012-05-01
In this contribution to EXA2011 congress, we present the status of the BMV ( Biréfringence Magnétique du Vide) experiment which is based on the use of a state-of-the-art optical resonant cavity and high pulsed magnetic fields, and it is hosted by the Laboratoire National des Champs Magnétiques Intenses in Toulouse, France.
Quantum vacuum magnetic birefringence
NASA Astrophysics Data System (ADS)
Berceau, Paul; Battesti, Rémy; Fouché, Mathilde; Frings, Paul; Nardone, Marc; Portugall, Oliver; Rikken, Geert L. J. A.; Rizzo, Carlo
In this contribution to EXA2011 congress, we present the status of the BMV (Biréfringence Magnétique du Vide) experiment which is based on the use of a state-of-the-art optical resonant cavity and high pulsed magnetic fields, and it is hosted by the Laboratoire National des Champs Magnétiques Intenses in Toulouse, France.
Quantum information approach to the azurite mineral frustrated quantum magnet
NASA Astrophysics Data System (ADS)
Batle, J.; Ooi, C. H. Raymond; Abutalib, M.; Farouk, Ahmed; Abdalla, S.
2016-07-01
Quantum correlations are almost impossible to address in bulk systems. Quantum measures extended only to a few number of parties can be discussed in practice. In the present work, we study nonlocality for a cluster of spins belonging to a mineral whose structure is that of a quantum magnet. We reproduce at a much smaller scale the experimental outcomes, and then, we study the role of quantum correlations there. A macroscopic entanglement witness has been introduced in order to reveal nonlocal quantum correlations between individual constituents of the azurite mineral at nonzero temperatures. The critical point beyond which entanglement is zero is found at T_c < 1 K.
O'Neal, Kenneth R.; Brinzari, Tatiana V.; Wright, Joshua B.; Ma, Chunli; Giri, Santanab; Schlueter, John A.; Wang, Qian; Jena, Puru; Liu, Zhenxian; Musfeldt, Janice L.
2014-08-13
Here, hydrogen bonding plays a foundational role in the life, earth, and chemical sciences, with its richness and strength depending on the situation. In molecular materials, these interactions determine assembly mechanisms, control superconductivity, and even permit magnetic exchange. In spite of its long-standing importance, exquisite control of hydrogen bonding in molecule-based magnets has only been realized in limited form and remains as one of the major challenges. Here, we report the discovery that pressure can tune the dimensionality of hydrogen bonding networks in CuF_{2}(H_{2}O)_{2}(3-chloropyridine) to induce magnetic switching. Specifically, we reveal how the development of exchange pathways under compression combined with an enhanced ab-plane hydrogen bonding network yields a three dimensional superexchange web between copper centers that triggers a reversible magnetic crossover. Similar pressure- and strain-driven crossover mechanisms involving coordinated motion of hydrogen bond networks may play out in other quantum magnets.
Pressure-induced magnetic crossover driven by hydrogen bonding in CuF2(H2O)2(3-chloropyridine)
O'Neal, Kenneth R.; Brinzari, Tatiana V.; Wright, Joshua B.; Ma, Chunli; Giri, Santanab; Schlueter, John A.; Wang, Qian; Jena, Puru; Liu, Zhenxian; Musfeldt, Janice L.
2014-08-13
Here, hydrogen bonding plays a foundational role in the life, earth, and chemical sciences, with its richness and strength depending on the situation. In molecular materials, these interactions determine assembly mechanisms, control superconductivity, and even permit magnetic exchange. In spite of its long-standing importance, exquisite control of hydrogen bonding in molecule-based magnets has only been realized in limited form and remains as one of the major challenges. Here, we report the discovery that pressure can tune the dimensionality of hydrogen bonding networks in CuF2(H2O)2(3-chloropyridine) to induce magnetic switching. Specifically, we reveal how the development of exchange pathways under compression combinedmore » with an enhanced ab-plane hydrogen bonding network yields a three dimensional superexchange web between copper centers that triggers a reversible magnetic crossover. Similar pressure- and strain-driven crossover mechanisms involving coordinated motion of hydrogen bond networks may play out in other quantum magnets.« less
Quantum nature of edge magnetism in graphene.
Golor, Michael; Wessel, Stefan; Schmidt, Manuel J
2014-01-31
It is argued that the subtle crossover from decoherence-dominated classical magnetism to fluctuation-dominated quantum magnetism is experimentally accessible in graphene nanoribbons. We show that the width of a nanoribbon determines whether the edge magnetism is on the classical side, on the quantum side, or in between. In the classical regime, decoherence is dominant and leads to static spin polarizations at the ribbon edges, which are well described by mean-field theories. The quantum Zeno effect is identified as the basic mechanism which is responsible for the spin polarization and thereby enables the application of graphene in spintronics. On the quantum side, however, the spin polarization is destroyed by dynamical processes. The great tunability of graphene magnetism thus offers a viable route for the study of the quantum-classical crossover.
Harmonic generation in magnetized quantum plasma
NASA Astrophysics Data System (ADS)
Kumar, Punit; Singh, Shiv; Singh, Abhisek Kumar
2016-05-01
A study of second harmonic generation by propagation of a linearly polarized electromagnetic wave through homogeneous high density quantum plasma in the presence of transverse magnetic field. The nonlinear current density and dispersion relations for the fundamental and second harmonic frequencies have been obtained using the recently developed quantum hydrodynamic (QHD) model. The effect of quantum Bohm potential, Fermi pressure and the electron spin have been taken into account. The second harmonic is found to be less dispersed than the first.
Decoherence in crystals of quantum molecular magnets.
Takahashi, S; Tupitsyn, I S; van Tol, J; Beedle, C C; Hendrickson, D N; Stamp, P C E
2011-07-20
Quantum decoherence is a central concept in physics. Applications such as quantum information processing depend on understanding it; there are even fundamental theories proposed that go beyond quantum mechanics, in which the breakdown of quantum theory would appear as an 'intrinsic' decoherence, mimicking the more familiar environmental decoherence processes. Such applications cannot be optimized, and such theories cannot be tested, until we have a firm handle on ordinary environmental decoherence processes. Here we show that the theory for insulating electronic spin systems can make accurate and testable predictions for environmental decoherence in molecular-based quantum magnets. Experiments on molecular magnets have successfully demonstrated quantum-coherent phenomena but the decoherence processes that ultimately limit such behaviour were not well constrained. For molecular magnets, theory predicts three principal contributions to environmental decoherence: from phonons, from nuclear spins and from intermolecular dipolar interactions. We use high magnetic fields on single crystals of Fe(8) molecular magnets (in which the Fe ions are surrounded by organic ligands) to suppress dipolar and nuclear-spin decoherence. In these high-field experiments, we find that the decoherence time varies strongly as a function of temperature and magnetic field. The theoretical predictions are fully verified experimentally, and there are no other visible decoherence sources. In these high fields, we obtain a maximum decoherence quality-factor of 1.49 × 10(6); our investigation suggests that the environmental decoherence time can be extended up to about 500 microseconds, with a decoherence quality factor of ∼6 × 10(7), by optimizing the temperature, magnetic field and nuclear isotopic concentrations.
Nuclear magnetic resonance quantum information processing
Serra, R. M.; Oliveira, I. S.
2012-01-01
For the past decade, nuclear magnetic resonance (NMR) has been established as a main experimental technique for testing quantum protocols in small systems. This Theme Issue presents recent advances and major challenges of NMR quantum information possessing (QIP), including contributions by researchers from 10 different countries. In this introduction, after a short comment on NMR-QIP basics, we briefly anticipate the contents of this issue. PMID:22946031
A cryogenic quantum gas scanning magnetic microscope
NASA Astrophysics Data System (ADS)
Turner, Richard; Naides, Matthew; Lai, Ruby; Disciacca, Jack; Lev, Benjamin
2014-05-01
Improved measurements of strongly correlated and topologically non-trivial systems open the path to a better fundamental understanding of these materials as well as the possibility for predictive design of new materials. We are working to demonstrate atom chip trapping of quantum gases to enable single-shot, large area imaging of electronic transport through these materials via detection of magnetic flux at the 10- 7 flux quantum level and below. Using the exquisite sensitivity of ultracold atoms in the form of either an atomic clock or Bose-Einstein condensate, the cryogenic atom chip technology we have recently demonstrated will provide a magnetic flux detection capability that surpasses other techniques while allowing sample temperatures spanning < 10 K to room temperature. We will report on experimental progress toward developing this novel quantum gas scanning magnetic microscope and describe our recent proposal to image topologically protected transport through a non-ideal topological insulator in a relatively model-independent fashion.
A cryogenic quantum gas scanning magnetic microscope
NASA Astrophysics Data System (ADS)
Turner, Richard; Naides, Matthew; Lai, Ruby; Disciacca, Jack; Lev, Benjamin
2014-05-01
Improved measurements of strongly correlated and topologically non-trivial systems open the path to a better fundamental understanding of these materials as well as the possibility for predictive design of new materials. We are working to demonstrate atom chip trapping of quantum gases to enable single-shot, large area imaging of electronic transport through these materials via detection of magnetic flux at the 10-7 flux quantum level and below. Using the exquisite sensitivity of ultracold atoms in the form of either an atomic clock or Bose-Einstein condensate, the cryogenic atom chip technology we have recently demonstrated will provide a magnetic flux detection capability that surpasses other techniques while allowing sample temperatures spanning < 10 K to room temperature. We will report on experimental progress toward developing this novel quantum gas scanning magnetic microscope and describe our recent proposal to image topologically protected transport through a non-ideal topological insulator in a relatively model-independent fashion.
A cryogenic quantum gas scanning magnetic microscope
NASA Astrophysics Data System (ADS)
Disciacca, Jack; Naides, Matthew; Turner, Richard; Lai, Ruby; Lev, Benjamin
2014-03-01
Improved measurements of strongly correlated and topologically non-trivial systems open the path to a better fundamental understanding of these materials as well as the possibility for predictive design of new materials. We are working to demonstrate atom chip trapping of quantum gases to enable single-shot, large area imaging of electronic transport through these materials via detection of magnetic flux at the 10-7 flux quantum level and below. Using the exquisite sensitivity of ultracold atoms in the form of either an atomic clock or Bose-Einstein condensate, the cryogenic atom chip technology we have recently demonstrated will provide a magnetic flux detection capability that surpasses other techniques while allowing sample temperatures spanning <10 K to room temperature. We will report on experimental progress toward developing this novel quantum gas scanning magnetic microscope and describe our recent proposal to image topologically protected transport through a non-ideal topological insulator in a relatively model-independent fashion.
A cryogenic quantum gas scanning magnetic microscope
NASA Astrophysics Data System (ADS)
Naides, Matthew; Turner, Richard; Lai, Ruby; Disciacca, Jack; Lev, Benjamin
2014-03-01
Atom chip trapping of quantum gases will enable single-shot, large area imaging of transport through strongly correlated and topologically non-trivial materials via detection of magnetic flux at the 10-7 flux quantum level and below. By harnessing the extreme sensitivity of atomic clocks and Bose-Einstein condensates to external perturbations, the cryogenic atom chip technology we have recently demonstrated [1] will provide a magnetic flux detection capability that surpasses other techniques, while allowing sample temperatures spanning <10 K to room temperature. We report on experimental progress toward developing this novel quantum gas scanning magnetic microscope [1] and describe our recent proposal [2] to image topologically protected transport through a non-ideal topological insulator in a relatively model-independent fashion. U.S. DOE, BES, Division of Materials Sciences and Engineering under award #DE-SC0001823.
Entangled quantum state of magnetic dipoles.
Ghosh, S; Rosenbaum, T F; Aeppli, G; Coppersmith, S N
2003-09-01
Free magnetic moments usually manifest themselves in Curie laws, where weak external magnetic fields produce magnetizations that vary as the reciprocal of the temperature (1/T). For a variety of materials that do not display static magnetism, including doped semiconductors and certain rare-earth intermetallics, the 1/T law is replaced by a power law T(-alpha) with alpha < 1. Here we show that a much simpler material system-namely, the insulating magnetic salt LiHo(x)Y(1-x)F(4)-can also display such a power law. Moreover, by comparing the results of numerical simulations of this system with susceptibility and specific-heat data, we show that both energy-level splitting and quantum entanglement are crucial to describing its behaviour. The second of these quantum mechanical effects-entanglement, where the wavefunction of a system with several degrees of freedom cannot be written as a product of wavefunctions for each degree of freedom-becomes visible for remarkably small tunnelling terms, and is activated well before tunnelling has visible effects on the spectrum. This finding is significant because it shows that entanglement, rather than energy-level redistribution, can underlie the magnetic behaviour of a simple insulating quantum spin system. PMID:12955135
``Magnetic'' refrigeration in synthetic quantum magnets
NASA Astrophysics Data System (ADS)
Zaletel, Michael; Yao, Norman
The advent of ultracold atomic systems has promised to expand upon our understanding of strongly correlated quantum ground states; by contrast to their material cousins, cold atomic experiments benefit from unique tools such as direct optical imaging and tunable short- and long-range interactions. However, despite advances in coherent quantum control, ultracold atoms remain much too hot. Although sub-nanokelvin temperatures are the norm in experiments, the entropy of the system remains extensively far above the ground state. One strategy to combat this is to shift the entropy elsewhere - for example, placing a gapless system near a gapped system can effectively ''cool'' the latter. In this talk, we will demonstrate that typical atomic systems can act as their own coolant. As an example, we consider a 1D optical lattice geometry where spin-1 atoms interact via a generic AKLT-type Hamiltonian. We will discuss why decreasing the density of atoms in one region is sufficient cool the complementary portion of the system to the ground state, wherein coherent edge dynamics are observed.
Quantum Criticality in an Organic Magnet
Stone, Matthew B; Broholm, C. L.; Reich, D. H.; Tchemyshyov, O.; Vorderwisch, P.; Harrison, N.
2006-01-01
Exchange interactions between S=1/2 sites in piperazinium hexachlorodicuprate produce a frustrated bilayer magnet with a singlet ground state. We have determined the field-temperature phase diagram by high field magnetization and neutron scattering experiments. There are two quantum critical points: H{sub c1}=7.5 T separates a quantum paramagnet phase from a three dimensional, antiferromagnetically ordered state while H{sub c2}=37 T marks the onset of a fully polarized state. The ordered phase, which we describe as a magnon Bose-Einstein condensate (BEC), is embedded in a quantum critical regime with short range correlations. A low temperature anomaly in the BEC phase boundary indicates that additional low energy features of the material become important near H{sub c1}.
Quantum transport of energy in controlled synthetic quantum magnets
NASA Astrophysics Data System (ADS)
Bermudez, Alejandro; Schaetz, Tobias
2016-08-01
We introduce a theoretical scheme that exploits laser cooling and phonon-mediated spin–spin interactions in crystals of trapped atomic ions to explore the transport of energy through a quantum magnet. We show how to implement an effective transport window to control the flow of energy through the magnet even in the absence of fermionic statistics for the carriers. This is achieved by shaping the density of states of the effective thermal reservoirs that arise from the interaction with the external bath of the modes of the electromagnetic field, and can be experimentally controlled by tuning the laser frequencies and intensities appropriately. The interplay of this transport window with the spin–spin interactions is exploited to build an analogue of the Coulomb-blockade effect in nano-scale electronic devices, and opens new possibilities to study quantum effects in energy transport.
Magnetic quantum phase transitions and entropy in Van Vleck magnet
NASA Astrophysics Data System (ADS)
Lavanov, G. Yu.; Kalita, V. M.; Ivanova, I. M.; Loktev, V. M.
2016-10-01
Field-induced magnetic quantum phase transitions in the Van Vleck paramagnet with easy-plane single-ion anisotropy and competing Ising exchange between ions with the spin S=1 have been studied theoretically. The description was made by minimizing the Lagrange function at zero temperature (T=0) and the free energy at T ≠ 0 . Stable and unstable solutions of equations corresponding to the case ψ0 = | 0 > asymptotically transform into those following from the Lagrange function at T=0. First-order phase transitions from the Van Vleck paramagnet state into the ferromagnet one were found to take place at a sufficiently high single-ion anisotropy. The entropy of such a magnet was shown to grow with its magnetization, as it occurs for antiferromagnets. At the point of quantum phase transition, the entropy has a jump, which magnitude depends on the ratio between the Ising exchange and anisotropy constants, as well as on the temperature. The described magnetic phase transition was supposed to be accompanied by the magnetocaloric effect. In the case when the Ising exchange dominates over the single-ion anisotropy, the magnetization reversal of ferromagnetic state by an external field was shown to be a phase transition of the first kind, which does not belong to orientational ones and which should be regarded as a quantum order-order phase transition.
Magnetic monopoles in quantum spin ice
NASA Astrophysics Data System (ADS)
Petrova, Olga; Moessner, Roderich; Sondhi, Shivaji
Typical spin ice materials can be modeled using classical Ising spins. The geometric frustration of the pyrochlore lattice causes the spins to satisfy ice rules, whereas a violation of the ice constraint constitutes an excitation. Flipping adjacent spins fractionalizes the excitation into two monopoles. Long range dipolar spin couplings result in Coulombic interactions between charges, while the leading effect of quantum fluctuations is to provide the monopoles with kinetic energy. We study the effect of adding quantum dynamics to spin ice, a well-known classical spin liquid, with a particular view of how to best detect its presence in experiment. For the weakly diluted quantum spin ice, we find a particularly crisp phenomenon, namely, the emergence of hydrogenic excited states in which a magnetic monopole is bound to a vacancy at various distances.
Topology-driven magnetic quantum phase transition in topological insulators.
Zhang, Jinsong; Chang, Cui-Zu; Tang, Peizhe; Zhang, Zuocheng; Feng, Xiao; Li, Kang; Wang, Li-Li; Chen, Xi; Liu, Chaoxing; Duan, Wenhui; He, Ke; Xue, Qi-Kun; Ma, Xucun; Wang, Yayu
2013-03-29
The breaking of time reversal symmetry in topological insulators may create previously unknown quantum effects. We observed a magnetic quantum phase transition in Cr-doped Bi2(SexTe1-x)3 topological insulator films grown by means of molecular beam epitaxy. Across the critical point, a topological quantum phase transition is revealed through both angle-resolved photoemission measurements and density functional theory calculations. We present strong evidence that the bulk band topology is the fundamental driving force for the magnetic quantum phase transition. The tunable topological and magnetic properties in this system are well suited for realizing the exotic topological quantum phenomena in magnetic topological insulators.
Magnetic quantum diesel engine in Ni2
NASA Astrophysics Data System (ADS)
Dong, C. D.; Lefkidis, G.; Hübner, W.
2013-12-01
Quantum Diesel cycles are numerically realized using the electronic states of a Ni2 dimer. The quantum nature and the complexity of the electronic structure of the Ni2 dimer result in new features in the evolution of the pressure as well as in the heat-work transformation. The multitude of internal degrees of freedom in the isobaric process in molecules can result in crossing of the two adiabatic processes in the P-V diagram. The interplay of heat and work, originating from thermal nonequilibrium effects, can lead to a thermal efficiency of up to 100%. The spin moment of the Ni2 can be decreased by the isobaric process. To link the molecular heat capacity to easily accessible experimental quantities, we also calculate the Kerr effect and the magnetic susceptibility at different temperatures and magnetic fields.
Quantum magnetism on kagome lattice
NASA Astrophysics Data System (ADS)
Hao, Zhihao
The spin 1/2 Heisenberg antiferromagnet on kagome (a planar lattice of corner sharing triangles) is one of the most celebrated models of a strongly correlated system. Despite intensive studies, the physics of its ground state and excitations remains unsettled. Recently, researchers successfully synthesized and characterized several new materials described by this model. It is hoped that the longstanding problem can be finally resolved through combined efforts of experimentalists, material scientists and theorists. In this thesis, we present a physical picture of the low energy physics of kagome. We demonstrate that there are N/3 fermionic particles on a kagome of N sites. The motion of these particles is strongly constrained. They are bound into small bosonic states by strong pair-wise attractions. The "antiparticle" also exists and a particle-antiparticle pair can be created at energy cost 0.218J. Low energy spin 1 excitations correspond to breaking a bound state into two free particles at energy cost 0.06J. This is the physical mechanism of the kagome spin gap. Our physical picture finds several applications. The dynamical structure factor of pair-breaking processes on kagome is computed. We assume the bound states are independent thanks to their small sizes. The result agrees well with the recent inelastic neutron scattering measurement conducted on herbertsmithite, a kagome antiferromagnet. In the second application, we study the effect of Dzyaloshinskii-Moriya (DM) interaction. DM interaction is important for low energy physics on kagome since the ground state of the dominate exchange interaction is highly degenerated. Through analytical and numerical arguments, it is determined that the vacuum become unstable to creation of particle-antiparticle pairs at critical strength D of DM interaction on the sawtooth chain, a chain of corner sharing triangles. We speculate that the mechanism is behind the numerically observed quantum phase transition at finite D on
Selectivity in multiple quantum nuclear magnetic resonance
Warren, W.S.
1980-11-01
The observation of multiple-quantum nuclear magnetic resonance transitions in isotropic or anisotropic liquids is shown to give readily interpretable information on molecular configurations, rates of motional processes, and intramolecular interactions. However, the observed intensity of high multiple-quantum transitions falls off dramatically as the number of coupled spins increases. The theory of multiple-quantum NMR is developed through the density matrix formalism, and exact intensities are derived for several cases (isotropic first-order systems and anisotropic systems with high symmetry) to shown that this intensity decrease is expected if standard multiple-quantum pulse sequences are used. New pulse sequences are developed which excite coherences and produce population inversions only between selected states, even though other transitions are simultaneously resonant. One type of selective excitation presented only allows molecules to absorb and emit photons in groups of n. Coherent averaging theory is extended to describe these selective sequences, and to design sequences which are selective to arbitrarily high order in the Magnus expansion. This theory and computer calculations both show that extremely good selectivity and large signal enhancements are possible.
Localized whistlers in magnetized spin quantum plasmas
Misra, A. P.; Brodin, G.; Marklund, M.; Shukla, P. K.
2010-11-15
The nonlinear propagation of electromagnetic (EM) electron-cyclotron waves (whistlers) along an external magnetic field, and their modulation by electrostatic small but finite amplitude ion-acoustic density perturbations are investigated in a uniform quantum plasma with intrinsic spin of electrons. The effects of the quantum force associated with the Bohm potential and the combined effects of the classical as well as the spin-induced ponderomotive forces (CPF and SPF, respectively) are taken into consideration. The latter modify the local plasma density in a self-consistent manner. The coupled modes of wave propagation is shown to be governed by a modified set of nonlinear Schroedinger-Boussinesq-like equations which admit exact solutions in form of stationary localized envelopes. Numerical simulation reveals the existence of large-scale density fluctuations that are self-consistently created by the localized whistlers in a strongly magnetized high density plasma. The conditions for the modulational instability (MI) and the value of its growth rate are obtained. Possible applications of our results, e.g., in strongly magnetized dense plasmas and in the next generation laser-solid density plasma interaction experiments are discussed.
Quantum transport in coupled resonators enclosed synthetic magnetic flux
NASA Astrophysics Data System (ADS)
Jin, L.
2016-07-01
Quantum transport properties are instrumental to understanding quantum coherent transport processes. Potential applications of quantum transport are widespread, in areas ranging from quantum information science to quantum engineering, and not restricted to quantum state transfer, control and manipulation. Here, we study light transport in a ring array of coupled resonators enclosed synthetic magnetic flux. The ring configuration, with an arbitrary number of resonators embedded, forms a two-arm Aharonov-Bohm interferometer. The influence of magnetic flux on light transport is investigated. Tuning the magnetic flux can lead to resonant transmission, while half-integer magnetic flux quantum leads to completely destructive interference and transmission zeros in an interferometer with two equal arms.
Quantum revivals and magnetization tunneling in effective spin systems
NASA Astrophysics Data System (ADS)
Krizanac, M.; Altwein, D.; Vedmedenko, E. Y.; Wiesendanger, R.
2016-03-01
Quantum mechanical objects or nano-objects have been proposed as bits for information storage. While time-averaged properties of magnetic, quantum-mechanical particles have been extensively studied experimentally and theoretically, experimental investigations of the real time evolution of magnetization in the quantum regime were not possible until recent developments in pump-probe techniques. Here we investigate the quantum dynamics of effective spin systems by means of analytical and numerical treatments. Particular attention is paid to the quantum revival time and its relation to the magnetization tunneling. The quantum revival time has been initially defined as the recurrence time of a total wave-function. Here we show that the quantum revivals of wave-functions and expectation values in spin systems may be quite different which gives rise to a more sophisticated definition of the quantum revival within the realm of experimental research. Particularly, the revival times for integer spins coincide which is not the case for half-integer spins. Furthermore, the quantum revival is found to be shortest for integer ratios between the on-site anisotropy and an external magnetic field paving the way to novel methods of anisotropy measurements. We show that the quantum tunneling of magnetization at avoided level crossing is coherent to the quantum revival time of expectation values, leading to a connection between these two fundamental properties of quantum mechanical spins.
Magnetic breakdown in double quantum wells
Harff, N.E. |; Simmons, J.A.; Klem, J.F.; Boebinger, G.S.; Pfeiffer, L.N.; West, K.W.
1996-08-01
The authors find that a sufficiently large perpendicular magnetic field (B{sub {perpendicular}}) causes magnetic breakdown (MB) in coupled double quantum wells (QWs) that are subject to an in-plane magnetic field (B{sub {parallel}}). B{sub {parallel}} shifts one QW dispersion curve with respect to that of the other QW, resulting in an anticrossing and an energy gap. When the gap is below the Fermi level the resulting Fermi surface (FS) consists of two components, a lens-shaped inner orbit and an hour-glass shaped outer orbit. B{sub {perpendicular}} causes Landau level formation and Shubnikov-de Haas (SdH) oscillations for each component of the FS. MB occurs when the magnetic forces from B{sub {perpendicular}} become dominant and the electrons move on free-electron circular orbits rather than on the lens and hour-glass orbits. MB is observed by identifying the peaks present in the Fourier power spectrum of the longitudinal resistance vs. 1/B{sub {perpendicular}} at constant B{sub {parallel}}, an arrangement achieved with an in-situ tilting sample holder. Results are presented for two strongly coupled GaAs/AlGaAs DQW samples.
Surface electromagnetic wave equations in a warm magnetized quantum plasma
Li, Chunhua; Yang, Weihong; Wu, Zhengwei; Chu, Paul K.
2014-07-15
Based on the single-fluid plasma model, a theoretical investigation of surface electromagnetic waves in a warm quantum magnetized inhomogeneous plasma is presented. The surface electromagnetic waves are assumed to propagate on the plane between a vacuum and a warm quantum magnetized plasma. The quantum magnetohydrodynamic model includes quantum diffraction effect (Bohm potential), and quantum statistical pressure is used to derive the new dispersion relation of surface electromagnetic waves. And the general dispersion relation is analyzed in some special cases of interest. It is shown that surface plasma oscillations can be propagated due to quantum effects, and the propagation velocity is enhanced. Furthermore, the external magnetic field has a significant effect on surface wave's dispersion equation. Our work should be of a useful tool for investigating the physical characteristic of surface waves and physical properties of the bounded quantum plasmas.
Magnetic resonance at the quantum limit
NASA Astrophysics Data System (ADS)
Bertet, Patrice
The detection and characterization of paramagnetic species by electron-spin resonance (ESR) spectroscopy has numerous applications in chemistry, biology, and materials science. Most ESR spectrometers rely on the inductive detection of the small microwave signals emitted by the spins during their Larmor precession into a microwave resonator in which they are embedded. Using the tools offered by circuit Quantum Electrodynamics (QED), namely high quality factor superconducting micro-resonators and Josephson parametric amplifiers that operate at the quantum limit when cooled at 20mK, we report an increase of the sensitivity of inductively detected ESR by 4 orders of magnitude over the state-of-the-art, enabling the detection of 1700 Bismuth donor spins in silicon with a signal-to-noise ratio of 1 in a single echo. We also demonstrate that the energy relaxation time of the spins is limited by spontaneous emission of microwave photons into the measurement line via the resonator, which opens the way to on-demand spin initialization via the Purcell effect. These results constitute a first step towards circuit QED experiments with magnetically coupled individual spins.
Quantum hair, magnetic monopoles and topology in quantum field theory
NASA Astrophysics Data System (ADS)
Liu, Hong
This dissertation is divided into two parts: In the first part, we present results obtained by a consideration of the non-classical energy momentum tensor associated with Euclidean Instantons outside the event horizon of black holes. We demonstrate how this allows an analytic estimate to be made of the effect of discrete quantum hair on the temperature of the black hole, in which the role of violations of the weak energy condition associated with instantons is made explicit, and in which the previous results are extended. Last, we demonstrate how the existence of a non-classical electric field outside the event horizon of black holes can be identified with a well-known effect in the Abelian-Higgs model in two dimensions. In this case, there is a one-to- one connection between the discrete charge of a black hole and a topological phase in two dimensions. In the second part, we find the spectrum of magnetic monopoles produced in the symmetry breaking SU(5) /to Glow = [ SU(3) × SU(2) × U(1)']/Z6 by constructing classical bound states of the fundamental monopoles. The spectrum of monopoles is found to correspond to the spectrum of one family of standard model fermions and hence, is a starting point for constructing the dual standard model. If the SU(3) factor now breaks down to Z3, the monopoles with non-trivial SU(3) charge get confined by strings in SU(3) singlets. We then discuss the fate of the monopoles if the [ SU(2) × U(1)']'Z2 factor breaks down to U(1)Q by a Higgs mechanism as in the electroweak model. Last, a more elaborate model is constructed to address the family replication problem. The breaking of a simple grand unified group to [ Glow × H1 × H2 × H3]/Z53 and then further to Glow, produces three families of stable monopoles each of whose magnetic quantum numbers correspond to the electric charges on the fermions of the Standard Model. Here Hi are simple Lie groups which each have a Z5 symmetry in common with Glow.
Control of quantum magnets by atomic exchange bias.
Yan, Shichao; Choi, Deung-Jang; Burgess, Jacob A J; Rolf-Pissarczyk, Steffen; Loth, Sebastian
2015-01-01
Mixing of discretized states in quantum magnets has a radical impact on their properties. Managing this effect is key for spintronics in the quantum limit. Magnetic fields can modify state mixing and, for example, mitigate destabilizing effects in single-molecule magnets. The exchange bias field has been proposed as a mechanism for localized control of individual nanomagnets. Here, we demonstrate that exchange coupling with the magnetic tip of a scanning tunnelling microscope provides continuous tuning of spin state mixing in an individual nanomagnet. By directly measuring spin relaxation time with electronic pump-probe spectroscopy, we find that the exchange interaction acts analogously to a local magnetic field that can be applied to a specific atom. It can be tuned in strength by up to several tesla and cancel external magnetic fields, thereby demonstrating the feasibility of complete control over individual quantum magnets with atomically localized exchange coupling.
Single Cell Magnetic Measurements with a Superconducting Quantum Interference Device
NASA Astrophysics Data System (ADS)
Palmstrom, Johanna C.; Arps, Jennifer; Dwyer, Bo; Kalisky, Beena; Kirtley, John R.; Moler, Kathryn A.; Qian, Lisa C.; Rosenberg, Aaron J.; Rutt, Brian; Tee, Sui Seng; Theis, Eric; Urbach, Elana; Wang, Yihua
2014-03-01
Magnetic nanoparticles play an important role in numerous biomedical applications such as magnetic resonance imaging and targeted drug delivery. There is a need for tools to characterize individual magnetic nanoparticles and the magnetic properties of individual cells. We use a scanning superconducting quantum interference device (SQUID) to observe the magnetic fields from single mammalian cells loaded with superparamagnetic iron oxide nanoparticles. We show that the SQUID is a useful tool for imaging biological magnetism and is capable of resolving cell to cell variations in magnetic dipole moments. We hope to correlate these magnetic images with real space imaging techniques such as optical and scanning electron microscopy. The visualization of single cell magnetism can be used to optimize biological magnetic imaging techniques, such as MRI, by quantifying the strength of magnetic dipole moments of in vitro magnetic labeling. This work is supported by a National Science Foundation Graduate Research Fellowship and a Gabilan Stanford Graduate Fellowship.
Reentrant formation of magnetic polarons in quantum dots
NASA Astrophysics Data System (ADS)
Pientka, J. M.; Oszwałdowski, R.; Petukhov, A. G.; Han, J. E.; Žutić, Igor
2012-10-01
We propose a model of magnetic polaron formation in semiconductor quantum dots doped with magnetic ions. A wetting layer serves as a reservoir of photogenerated holes, which can be trapped by the adjacent quantum dots. For certain hole densities, the temperature dependence of the magnetization induced by the trapped holes is reentrant: it disappears for some temperature range and reappears at higher temperatures. We demonstrate that this peculiar effect is not an artifact of the mean-field approximation and persists after statistical spin fluctuations are accounted for. We predict fingerprints of reentrant magnetic polarons in photoluminescence spectra.
Barocaloric effect and the pressure induced solid state refrigerator
NASA Astrophysics Data System (ADS)
de Oliveira, N. A.
2011-03-01
The current refrigerators are based on the heating and cooling of fluids under external pressure variation. The great inconvenience of this refrigeration technology is the damage caused to the environment by the refrigerant fluids. In this paper, we discuss the magnetic barocaloric effect, i.e., the heating or cooling of magnetic materials under pressure variation and its application in the construction of refrigerators using solid magnetic compounds as refrigerant materials and pressure as the external agent. The discussion presented in this paper points out that such a pressure induced solid state refrigerator can be very interesting because it is not harmful to the environment and can exhibit a good performance.
Electrons, Stern-Gerlach magnets, and quantum mechanical propagation
NASA Astrophysics Data System (ADS)
Batelaan, H.
2002-03-01
Quantum corrections to Newton's equations are obtained and used to illustrate that classical dynamics is embedded explicitly in quantum dynamics. Originally, the resultant set of dynamical equations has been used to shed light on quantum chaos. We show that the method can provide insight into the dynamics of free particles and the harmonic oscillator. We then use it to determine whether Stern-Gerlach magnets can be constructed for free electrons.
Tateiwa, Naoyuki; Haga, Yoshinori; Matsuda, Tatsuma D; Fisk, Zachary
2012-05-01
A miniature ceramic anvil high pressure cell (mCAC) was earlier designed by us for magnetic measurements at pressures up to 7.6 GPa in a commercial superconducting quantum interference magnetometer [N. Tateiwa et al., Rev. Sci. Instrum. 82, 053906 (2011)]. Here, we describe methods to generate pressures above 10 GPa in the mCAC. The efficiency of the pressure generation is sharply improved when the Cu-Be gasket is sufficiently preindented. The maximum pressure for the 0.6 mm culet anvils is 12.6 GPa when the Cu-Be gasket is preindented from the initial thickness of 300-60 μm. The 0.5 mm culet anvils were also tested with a rhenium gasket. The maximum pressure attainable in the mCAC is about 13 GPa. The present cell was used to study YbCu(2)Si(2) which shows a pressure induced transition from the non-magnetic to magnetic phases at 8 GPa. We confirm a ferromagnetic transition from the dc magnetization measurement at high pressure. The mCAC can detect the ferromagnetic ordered state whose spontaneous magnetic moment is smaller than 1 μ(B) per unit cell. The high sensitivity for magnetic measurements in the mCAC may result from the simplicity of cell structure. The present study shows the availability of the mCAC for precise magnetic measurements at pressures above 10 GPa.
NASA Astrophysics Data System (ADS)
Herzog, F.; Heedt, S.; Goerke, S.; Ibrahim, A.; Rupprecht, B.; Heyn, Ch; Hardtdegen, H.; Schäpers, Th; Wilde, M. A.; Grundler, D.
2016-02-01
We report on the magnetization of ensembles of etched quantum dots with a lateral diameter of 460 nm, which we prepared from InGaAs/InP heterostructures. The quantum dots exhibit 1/B-periodic de-Haas-van-Alphen-type oscillations in the magnetization M(B) for external magnetic fields B > 2 T, measured by torque magnetometry at 0.3 K. We compare the experimental data to model calculations assuming different confinement potentials and including ensemble broadening effects. The comparison shows that a hard wall potential with an edge depletion width of 100 nm explains the magnetic behavior. Beating patterns induced by Rashba spin-orbit interaction (SOI) as measured in unpatterned and nanopatterned InGaAs/InP heterostructures are not observed for the quantum dots. From our model we predict that signatures of SOI in the magnetization could be observed in larger dots in tilted magnetic fields.
Fractional quantum Hall effect in a tilted magnetic field
NASA Astrophysics Data System (ADS)
Papić, Z.
2013-06-01
We discuss the orbital effect of a tilted magnetic field on the quantum Hall effect in parabolic quantum wells. Many-body states realized at the fractional (1)/(3) and (1)/(2) filling of the second electronic subband are studied using finite-size exact diagonalization. In both cases, we obtain the phase diagram consisting of a fractional quantum Hall fluid phase that persists for moderate tilts, and eventually undergoes a direct transition to the stripe phase. It is shown that tilting of the field probes the geometrical degree of freedom of fractional quantum Hall fluids, and can be partly related to the effect of band-mass anisotropy.
Surface waves in magnetized quantum electron-positron plasmas
NASA Astrophysics Data System (ADS)
Misra, A. P.; Ghosh, N. K.; Shukla, P. K.
2010-02-01
The dispersion properties of electrostatic surface waves propagating along the interface between a quantum magnetoplasma composed of electrons and positrons, and vacuum are studied by using a quantum magnetohydrodynamic plasma model. The general dispersion relation for arbitrary orientation of the magnetic field and the propagation vector is derived and analyzed in some special cases of interest (viz. when the magnetic field is directed parallel and perpendicular to the boundary surface). It is found that the quantum effects facilitate the propagation of electrostatic surface modes in a dense magnetoplasma. The effect of the external magnetic field is found to increase the frequency of the quantum surface wave. The existence of a singular wave on the boundary surface is also proved, and its properties are analyzed numerically. It is shown that the new wave characteristics appear due to the Rayleigh type of the wave.
Decoherence induced by magnetic impurities in a quantum hall system
Kagalovsky, V.; Chudnovskiy, A. L.
2013-04-15
Scattering by magnetic impurities is known to destroy coherence of electron motion in metals and semiconductors. We investigate the decoherence introduced in a single act of electron scattering by a magnetic impurity in a quantum Hall system. For this, we introduce a fictitious nonunitary scattering matrix for electrons that reproduces the exactly calculated scattering probabilities. The strength of decoherence is identified by the deviation of eigenvalues of the product from unity. Using the fictitious scattering matrix, we estimate the width of the metallic region at the quantum Hall effect inter-plateau transition and its dependence on the exchange coupling strength and the degree of polarization of magnetic impurities.
Orbital Magnetization of Quantum Spin Hall Insulator Nanoparticles.
Potasz, P; Fernández-Rossier, J
2015-09-01
Both spin and orbital degrees of freedom contribute to the magnetic moment of isolated atoms. However, when inserted in crystals, atomic orbital moments are quenched because of the lack of rotational symmetry that protects them when isolated. Thus, the dominant contribution to the magnetization of magnetic materials comes from electronic spin. Here we show that nanoislands of quantum spin Hall insulators can host robust orbital edge magnetism whenever their highest occupied Kramers doublet is singly occupied, upgrading the spin edge current into a charge current. The resulting orbital magnetization scales linearly with size, outweighing the spin contribution for islands of a few nm in size. This linear scaling is specific of the Dirac edge states and very different from Schrodinger electrons in quantum rings. By modeling Bi(111) flakes, whose edge states have been recently observed, we show that orbital magnetization is robust with respect to disorder, thermal agitation, shape of the island, and crystallographic direction of the edges, reflecting its topological protection.
Magnetic quantum dots and rings in two dimensions
NASA Astrophysics Data System (ADS)
Downing, C. A.; Portnoi, M. E.
2016-07-01
We consider the motion of electrons confined to a two-dimensional plane with an externally applied perpendicular inhomogeneous magnetic field, both with and without a Coulomb potential. We find that as long as the magnetic field is slowly decaying, bound states in magnetic quantum dots are indeed possible. Several example cases of such magnetic quantum dots are considered in which one can find the eigenvalues and eigenfunctions in closed form, including two hitherto unknown quasi-exactly-solvable models treated with confluent and biconfluent Heun polynomials. It is shown how a modulation of the strength of the magnetic field can exclude magnetic vortexlike states, rotating with a certain angular momenta and possessing a definite spin orientation, from forming. This indicates one may induce localization-delocalization transitions and suggests a mechanism for spin separation.
Quantum phases in intrinsic Josephson junctions: Quantum magnetism analogy
NASA Astrophysics Data System (ADS)
Machida, Masahiko; Kobayashi, Keita; Koyama, Tomio
2013-08-01
We explore quantum phases in intrinsic Josephson junction (IJJ) stacks, whose in-plane area is so small that the capacitive coupling has a dominant role in the superconducting phase dynamics. In such cases, the effective Hamiltonian for the superconducting phase can be mapped onto that of one-dimensional ferromagnetically-interacting spin model, whose spin length S depends on the magnitude of the on-site Coulomb repulsion. The ferromagnetic model for IJJ’s prefers synchronized quantum features in contrast to the antiferromagnetically-interacting model in the conventional Josephson junction arrays.
Imaging Micrometer Scale Rock Magnetism Using a Quantum Diamond Microscope
NASA Astrophysics Data System (ADS)
Fu, R. R.; Glenn, D. R.; Le Sage, D.; Andrade Lima, E.; Weiss, B. P.; Walsworth, R. L.
2014-12-01
Optically-detected magnetometry using quantum defects in diamond, known as nitrogen-vacancy (NV) color centers, is an emerging technology that allows high sensitivity and high resolution mapping of magnetic fields. Recent measurements of live magnetotactic bacteria demonstrate that such a "quantum diamond microscope" can image individual magnetic sources with <500 nm resolution, >1 mm field-of-view, and magnetic moment sensitivity <10-16 A m2 under ambient temperatures and pressures. The unprecedented combination of spatial resolution and magnetic sensitivity of the quantum diamond microscope permits magnetic analyses of previously inaccessible geologic samples in which the regions of interest are mixed with undesirable magnetic field sources at the <<100 µm scale. Here we apply this technique to chondritic meteorites, primordial aggregates formed during the accretional phase of the solar system. These meteorites consist of fine-grained matrix mixed with chondrules and other inclusions with characteristic sizes of 0.1 - 1 mm. Each chondrule records a unique magnetic history and potentially constrains nebular magnetic fields, which likely played a key role in accretion disk dynamics. The quantum diamond microscope is unique in its ability to resolve the magnetic signal of single inclusions from surrounding material. We applied the quantum diamond microscope to a variety of natural and artificial samples. Magnetic field maps of a single chondrule from the Allende CV carbonaceous chondrite (Fig. 1) show that the strongest magnetic sources are located in its 20 μm thick rim. Magnetic field sources in the chondrule interior occur in the mesostasis as isolated 10-100 μm patches that generate magnetic fields ~10 times weaker than the rim. These maps highlight the importance of spatial resolution for paleomagnetic measurements of chondrites; lower resolution measurements would permit the nearby rim material to dominate the magnetic signal, precluding accurate recovery
NASA Astrophysics Data System (ADS)
Holovatsky, V.; Bernik, I.; Yakhnevych, M.
2016-09-01
The effect of magnetic field on electron energy spectrum, wave functions and probabilities of intraband quantum transitions in multilayered spherical quantum-dot-quantum-well (QDQW) CdSe/ZnS/CdSe/ZnS is studied. Computations are performed in the framework of the effective mass approximation and rectangular potential barriers model. The wave functions are expanded over the complete basis of functions obtained as exact solutions of the Schrodinger equation for the electron in QDQW without the magnetic field. It is shown that magnetic field takes off the spectrum degeneration with respect to the magnetic quantum number and changes the localization of electron in the nanostructure. The field stronger effects on the spherically-symmetric states, especially in the case of electron location in the outer potential well. The magnetic field changes more the radial distribution of probability of electron location in QDQW than the angular one. The oscillator strengths of intraband quantum transitions are calculated as functions of the magnetic field induction and their selection rules are established.
Magnetic torque anomaly in the quantum limit of Weyl semimetals
NASA Astrophysics Data System (ADS)
Moll, Philip J. W.; Potter, Andrew C.; Nair, Nityan L.; Ramshaw, B. J.; Modic, K. A.; Riggs, Scott; Zeng, Bin; Ghimire, Nirmal J.; Bauer, Eric D.; Kealhofer, Robert; Ronning, Filip; Analytis, James G.
2016-08-01
Electrons in materials with linear dispersion behave as massless Weyl- or Dirac-quasiparticles, and continue to intrigue due to their close resemblance to elusive ultra-relativistic particles as well as their potential for future electronics. Yet the experimental signatures of Weyl-fermions are often subtle and indirect, in particular if they coexist with conventional, massive quasiparticles. Here we show a pronounced anomaly in the magnetic torque of the Weyl semimetal NbAs upon entering the quantum limit state in high magnetic fields. The torque changes sign in the quantum limit, signalling a reversal of the magnetic anisotropy that can be directly attributed to the topological nature of the Weyl electrons. Our results establish that anomalous quantum limit torque measurements provide a direct experimental method to identify and distinguish Weyl and Dirac systems.
Magnetic torque anomaly in the quantum limit of Weyl semimetals.
Moll, Philip J W; Potter, Andrew C; Nair, Nityan L; Ramshaw, B J; Modic, K A; Riggs, Scott; Zeng, Bin; Ghimire, Nirmal J; Bauer, Eric D; Kealhofer, Robert; Ronning, Filip; Analytis, James G
2016-01-01
Electrons in materials with linear dispersion behave as massless Weyl- or Dirac-quasiparticles, and continue to intrigue due to their close resemblance to elusive ultra-relativistic particles as well as their potential for future electronics. Yet the experimental signatures of Weyl-fermions are often subtle and indirect, in particular if they coexist with conventional, massive quasiparticles. Here we show a pronounced anomaly in the magnetic torque of the Weyl semimetal NbAs upon entering the quantum limit state in high magnetic fields. The torque changes sign in the quantum limit, signalling a reversal of the magnetic anisotropy that can be directly attributed to the topological nature of the Weyl electrons. Our results establish that anomalous quantum limit torque measurements provide a direct experimental method to identify and distinguish Weyl and Dirac systems. PMID:27545105
Magnetic torque anomaly in the quantum limit of Weyl semimetals
Moll, Philip J. W.; Potter, Andrew C.; Nair, Nityan L.; Ramshaw, B. J.; Modic, K. A.; Riggs, Scott; Zeng, Bin; Ghimire, Nirmal J.; Bauer, Eric D.; Kealhofer, Robert; Ronning, Filip; Analytis, James G.
2016-01-01
Electrons in materials with linear dispersion behave as massless Weyl- or Dirac-quasiparticles, and continue to intrigue due to their close resemblance to elusive ultra-relativistic particles as well as their potential for future electronics. Yet the experimental signatures of Weyl-fermions are often subtle and indirect, in particular if they coexist with conventional, massive quasiparticles. Here we show a pronounced anomaly in the magnetic torque of the Weyl semimetal NbAs upon entering the quantum limit state in high magnetic fields. The torque changes sign in the quantum limit, signalling a reversal of the magnetic anisotropy that can be directly attributed to the topological nature of the Weyl electrons. Our results establish that anomalous quantum limit torque measurements provide a direct experimental method to identify and distinguish Weyl and Dirac systems. PMID:27545105
Magnetic polyoxometalates: from molecular magnetism to molecular spintronics and quantum computing.
Clemente-Juan, Juan M; Coronado, Eugenio; Gaita-Ariño, Alejandro
2012-11-21
In this review we discuss the relevance of polyoxometalate (POM) chemistry to provide model objects in molecular magnetism. We present several potential applications in nanomagnetism, in particular, in molecular spintronics and quantum computing.
Quantum hall effect at low magnetic fields
Huckestein
2000-04-01
The temperature and scale dependence of resistivities in the standard scaling theory of the integer quantum Hall effect is discussed. It is shown that recent experiments, claiming to observe a discrepancy with the global phase diagram of the quantum Hall effect, are in fact in agreement with the standard theory. The apparent low-field transition observed in the experiments is identified as a crossover due to weak localization and a strong reduction of the conductivity when Landau quantization becomes dominant.
The quantum dusty magnetosonic solitary wave in magnetized plasma
Wang Yunliang; Qiu Hong; Wang Fengping; Lu Yanzhen; Zhou Zhongxiang
2012-01-15
The effects of quantum statistic and quantum diffraction on the weakly two-dimensional fast quantum dusty magnetosonic wave propagating perpendicular to the external magnetic field are investigated by considering the inertialess electron, inertialess ion, and inertial cold dust in the low frequency limit. A Kadomstev-Petviashvili equation is derived for the magnetosonic solitary wave by using reductive perturbation method. The results show that the amplitude of soliton increases with the increasing of quantum diffraction effects of both electrons and ions, while the amplitude of the soliton decreases with the increasing of the quantum statistic effects. By using the numerical investigations, the interaction law of the nontrivial line-solitons with rich web structure in the interaction area among the line-solitons is studied by the Wronskian determinant method, which shows that there is no exchange of the energy, the momentum, and the angular momentum in the interaction.
Simulations of magnetic field gradients due to micro-magnets on a triple quantum dot circuit
Poulin-Lamarre, G.; Bureau-Oxton, C.; Kam, A.; Zawadzki, P.; Aers, G.; Studenikin, S.; Pioro-Ladrière, M.; Sachrajda, A. S.
2013-12-04
To quantify the effects of local magnetic fields on triple quantum dots, the Heisenberg Hamiltonian has been diagonalized for three electrons coupled via the exchange interaction. In particular, we have investigated different geometries of micro-magnets located on top of the triple dot in order to optimize the field gradient characteristics. In this paper, we focus on two geometries which are candidates for an addressable EDSR triple quantum dot device.
Magnetic rigid rotor in the quantum regime: Theoretical toolbox
NASA Astrophysics Data System (ADS)
Rusconi, Cosimo C.; Romero-Isart, Oriol
2016-02-01
We describe the quantum dynamics of a magnetic rigid rotor in the mesoscopic scale where the Einstein-De Haas effect is predominant. In particular, we consider a single-domain magnetic nanoparticle with uniaxial anisotropy in a magnetic trap. Starting from the basic Hamiltonian of the system under the macrospin approximation, we derive a bosonized Hamiltonian describing the center-of-mass motion, the total angular momentum, and the macrospin degrees of freedom of the particle treated as a rigid body. This bosonized Hamiltonian can be approximated by a simple quadratic Hamiltonian that captures the rich physics of a nanomagnet tightly confined in position, nearly not spinning, and with its macrospin antialigned to the magnetic field. The theoretical tools derived and used here can be applied to other quantum mechanical rigid rotors.
Pressure induced crystallization in amorphous silicon
NASA Astrophysics Data System (ADS)
Pandey, K. K.; Garg, Nandini; Shanavas, K. V.; Sharma, Surinder M.; Sikka, S. K.
2011-06-01
We have investigated the high pressure behavior of amorphous silicon (a-Si) using x-ray diffraction and Raman scattering techniques. Our experiments show that a-Si undergoes a polyamorphous transition from the low density amorphous to the high density amorphous phase, followed by pressure induced crystallization to the primitive hexagonal (ph) phase. On the release path, the sequence of observed phase transitions depends on whether the pressure is reduced slowly or rapidly. Using the results of our first principles calculations, pressure induced preferential crystallization to the ph phase is explained in terms of a thermodynamic model based on phenomenological random nucleation and the growth process.
On the quantumness of correlations in nuclear magnetic resonance.
Soares-Pinto, D O; Auccaise, R; Maziero, J; Gavini-Viana, A; Serra, R M; Céleri, L C
2012-10-13
Nuclear magnetic resonance (NMR) was successfully employed to test several protocols and ideas in quantum information science. In most of these implementations, the existence of entanglement was ruled out. This fact introduced concerns and questions about the quantum nature of such bench tests. In this paper, we address some issues related to the non-classical aspects of NMR systems. We discuss some experiments where the quantum aspects of this system are supported by quantum correlations of separable states. Such quantumness, beyond the entanglement-separability paradigm, is revealed via a departure between the quantum and the classical versions of information theory. In this scenario, the concept of quantum discord seems to play an important role. We also present an experimental implementation of an analogue of the single-photon Mach-Zehnder interferometer employing two nuclear spins to encode the interferometric paths. This experiment illustrates how non-classical correlations of separable states may be used to simulate quantum dynamics. The results obtained are completely equivalent to the optical scenario, where entanglement (between two field modes) may be present.
A quantum phase transition in a quantum external field: Superposing two magnetic phases
Rams, Marek M.; Zwolak, Michael; Damski, Bogdan
2012-01-01
We study an Ising chain undergoing a quantum phase transition in a quantum magnetic field. Such a field can be emulated by coupling the chain to a central spin initially in a superposition state. We show that – by adiabatically driving such a system – one can prepare a quantum superposition of any two ground states of the Ising chain. In particular, one can end up with the Ising chain in a superposition of ferromagnetic and paramagnetic phases – a scenario with no analogue in prior studies of quantum phase transitions. Remarkably, the resulting magnetization of the chain encodes the position of the critical point and universal critical exponents, as well as the ground state fidelity. PMID:22977730
Coherent radiation by quantum dots and magnetic nanoclusters
Yukalov, V. I.; Yukalova, E. P.
2014-03-31
The assemblies of either quantum dots or magnetic nanoclusters are studied. It is shown that such assemblies can produce coherent radiation. A method is developed for solving the systems of nonlinear equations describing the dynamics of such assemblies. The method is shown to be general and applicable to systems of different physical nature. Despite mathematical similarities of dynamical equations, the physics of the processes for quantum dots and magnetic nanoclusters is rather different. In a quantum dot assembly, coherence develops due to the Dicke effect of dot interactions through the common radiation field. For a system of magnetic clusters, coherence in the spin motion appears due to the Purcell effect caused by the feedback action of a resonator. Self-organized coherent spin radiation cannot arise without a resonator. This principal difference is connected with the different physical nature of dipole forces between the objects. Effective dipole interactions between the radiating quantum dots, appearing due to photon exchange, collectivize the dot radiation. While the dipolar spin interactions exist from the beginning, yet before radiation, and on the contrary, they dephase spin motion, thus destroying the coherence of moving spins. In addition, quantum dot radiation exhibits turbulent photon filamentation that is absent for radiating spins.
Spin-orbit coupled molecular quantum magnetism realized in inorganic solid.
Park, Sang-Youn; Do, S-H; Choi, K-Y; Kang, J-H; Jang, Dongjin; Schmidt, B; Brando, Manuel; Kim, B-H; Kim, D-H; Butch, N P; Lee, Seongsu; Park, J-H; Ji, Sungdae
2016-01-01
Molecular quantum magnetism involving an isolated spin state is of particular interest due to the characteristic quantum phenomena underlying spin qubits or molecular spintronics for quantum information devices, as demonstrated in magnetic metal-organic molecular systems, the so-called molecular magnets. Here we report the molecular quantum magnetism realized in an inorganic solid Ba3Yb2Zn5O11 with spin-orbit coupled pseudospin-½ Yb(3+) ions. The magnetization represents the magnetic quantum values of an isolated Yb4 tetrahedron with a total (pseudo)spin 0, 1 and 2. Inelastic neutron scattering results reveal that a large Dzyaloshinsky-Moriya interaction originating from strong spin-orbit coupling of Yb 4f is a key ingredient to explain magnetic excitations of the molecular magnet states. The Dzyaloshinsky-Moriya interaction allows a non-adiabatic quantum transition between avoided crossing energy levels, and also results in unexpected magnetic behaviours in conventional molecular magnets. PMID:27650796
Spin–orbit coupled molecular quantum magnetism realized in inorganic solid
Park, Sang-Youn; Do, S.-H.; Choi, K.-Y.; Kang, J.-H.; Jang, Dongjin; Schmidt, B.; Brando, Manuel; Kim, B.-H.; Kim, D.-H.; Butch, N. P.; Lee, Seongsu; Park, J.-H.; Ji, Sungdae
2016-01-01
Molecular quantum magnetism involving an isolated spin state is of particular interest due to the characteristic quantum phenomena underlying spin qubits or molecular spintronics for quantum information devices, as demonstrated in magnetic metal–organic molecular systems, the so-called molecular magnets. Here we report the molecular quantum magnetism realized in an inorganic solid Ba3Yb2Zn5O11 with spin–orbit coupled pseudospin-½ Yb3+ ions. The magnetization represents the magnetic quantum values of an isolated Yb4 tetrahedron with a total (pseudo)spin 0, 1 and 2. Inelastic neutron scattering results reveal that a large Dzyaloshinsky–Moriya interaction originating from strong spin–orbit coupling of Yb 4f is a key ingredient to explain magnetic excitations of the molecular magnet states. The Dzyaloshinsky–Moriya interaction allows a non-adiabatic quantum transition between avoided crossing energy levels, and also results in unexpected magnetic behaviours in conventional molecular magnets. PMID:27650796
Spin-orbit coupled molecular quantum magnetism realized in inorganic solid.
Park, Sang-Youn; Do, S-H; Choi, K-Y; Kang, J-H; Jang, Dongjin; Schmidt, B; Brando, Manuel; Kim, B-H; Kim, D-H; Butch, N P; Lee, Seongsu; Park, J-H; Ji, Sungdae
2016-09-21
Molecular quantum magnetism involving an isolated spin state is of particular interest due to the characteristic quantum phenomena underlying spin qubits or molecular spintronics for quantum information devices, as demonstrated in magnetic metal-organic molecular systems, the so-called molecular magnets. Here we report the molecular quantum magnetism realized in an inorganic solid Ba3Yb2Zn5O11 with spin-orbit coupled pseudospin-½ Yb(3+) ions. The magnetization represents the magnetic quantum values of an isolated Yb4 tetrahedron with a total (pseudo)spin 0, 1 and 2. Inelastic neutron scattering results reveal that a large Dzyaloshinsky-Moriya interaction originating from strong spin-orbit coupling of Yb 4f is a key ingredient to explain magnetic excitations of the molecular magnet states. The Dzyaloshinsky-Moriya interaction allows a non-adiabatic quantum transition between avoided crossing energy levels, and also results in unexpected magnetic behaviours in conventional molecular magnets.
Spin-orbit coupled molecular quantum magnetism realized in inorganic solid
NASA Astrophysics Data System (ADS)
Park, Sang-Youn; Do, S.-H.; Choi, K.-Y.; Kang, J.-H.; Jang, Dongjin; Schmidt, B.; Brando, Manuel; Kim, B.-H.; Kim, D.-H.; Butch, N. P.; Lee, Seongsu; Park, J.-H.; Ji, Sungdae
2016-09-01
Molecular quantum magnetism involving an isolated spin state is of particular interest due to the characteristic quantum phenomena underlying spin qubits or molecular spintronics for quantum information devices, as demonstrated in magnetic metal-organic molecular systems, the so-called molecular magnets. Here we report the molecular quantum magnetism realized in an inorganic solid Ba3Yb2Zn5O11 with spin-orbit coupled pseudospin-1/2 Yb3+ ions. The magnetization represents the magnetic quantum values of an isolated Yb4 tetrahedron with a total (pseudo)spin 0, 1 and 2. Inelastic neutron scattering results reveal that a large Dzyaloshinsky-Moriya interaction originating from strong spin-orbit coupling of Yb 4f is a key ingredient to explain magnetic excitations of the molecular magnet states. The Dzyaloshinsky-Moriya interaction allows a non-adiabatic quantum transition between avoided crossing energy levels, and also results in unexpected magnetic behaviours in conventional molecular magnets.
Double-layer shocks in a magnetized quantum plasma.
Misra, A P; Samanta, S
2010-09-01
The formation of small but finite amplitude electrostatic shocks in the propagation of quantum ion-acoustic waves obliquely to an external magnetic field is reported in a quantum electron-positron-ion plasma. Such shocks are seen to have double-layer (DL) structures composed of the compressive and accompanying rarefactive slow-wave fronts. Existence of such DL shocks depends critically on the quantum coupling parameter H associated with the Bohm potential and the positron to electron density ratio δ . The profiles may, however, steepen initially and reach a steady state with a number of solitary waves in front of the shocks. Such novel DL shocks could be a good candidate for particle acceleration in intense laser-solid density plasma interaction experiments as well as in compact astrophysical objects, e.g., magnetized white dwarfs.
Double-layer shocks in a magnetized quantum plasma
NASA Astrophysics Data System (ADS)
Misra, A. P.; Samanta, S.
2010-09-01
The formation of small but finite amplitude electrostatic shocks in the propagation of quantum ion-acoustic waves obliquely to an external magnetic field is reported in a quantum electron-positron-ion plasma. Such shocks are seen to have double-layer (DL) structures composed of the compressive and accompanying rarefactive slow-wave fronts. Existence of such DL shocks depends critically on the quantum coupling parameter H associated with the Bohm potential and the positron to electron density ratio δ . The profiles may, however, steepen initially and reach a steady state with a number of solitary waves in front of the shocks. Such novel DL shocks could be a good candidate for particle acceleration in intense laser-solid density plasma interaction experiments as well as in compact astrophysical objects, e.g., magnetized white dwarfs.
Magnetic resonance detection of individual proton spins using quantum reporters.
Sushkov, A O; Lovchinsky, I; Chisholm, N; Walsworth, R L; Park, H; Lukin, M D
2014-11-01
We demonstrate a method of magnetic resonance imaging with single nuclear-spin sensitivity under ambient conditions. Our method employs isolated electronic-spin quantum bits (qubits) as magnetic resonance "reporters" on the surface of high purity diamond. These spin qubits are localized with nanometer-scale uncertainty, and their quantum state is coherently manipulated and measured optically via a proximal nitrogen-vacancy color center located a few nanometers below the diamond surface. This system is then used for sensing, coherent coupling, and imaging of individual proton spins on the diamond surface with angstrom resolution. Our approach may enable direct structural imaging of complex molecules that cannot be accessed from bulk studies. It realizes a new platform for probing novel materials, monitoring chemical reactions, and manipulation of complex systems on surfaces at a quantum level. PMID:25415924
Quasiparticle-continuum level repulsion in a quantum magnet
Plumb, K. W.; Hwang, Kyusung; Qiu, Y.; Harriger, Leland W.; Granroth, G. Â E.; Kolesnikov, Alexander I.; Shu, G. J.; Chou, F. C.; Rüegg, Ch.; Kim, Yong Baek; et al
2015-11-30
When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticles in solids. But, little is known about the level repulsion when more than two quasiparticles are present; for example, in a strongly interacting quantum system where a quasiparticle can spontaneously decay into a many-particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. Here,more » we observe a renormalization of the quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states, in our fine-resolution neutron spectroscopy study of magnetic quasiparticles in the frustrated quantum magnet BiCu2PO6.« less
Quasiparticle-continuum level repulsion in a quantum magnet
Plumb, K. W.; Hwang, Kyusung; Qiu, Y.; Harriger, Leland W.; Granroth, G. Â E.; Kolesnikov, Alexander I.; Shu, G. J.; Chou, F. C.; Rüegg, Ch.; Kim, Yong Baek; Kim, Young-June
2015-11-30
When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticles in solids. But, little is known about the level repulsion when more than two quasiparticles are present; for example, in a strongly interacting quantum system where a quasiparticle can spontaneously decay into a many-particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. Here, we observe a renormalization of the quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states, in our fine-resolution neutron spectroscopy study of magnetic quasiparticles in the frustrated quantum magnet BiCu_{2}PO_{6}.
Quasiparticle-continuum level repulsion in a quantum magnet
NASA Astrophysics Data System (ADS)
Plumb, K. W.; Hwang, Kyusung; Qiu, Y.; Harriger, Leland W.; Granroth, G. E.; Kolesnikov, Alexander I.; Shu, G. J.; Chou, F. C.; Rüegg, Ch.; Kim, Yong Baek; Kim, Young-June
2016-03-01
When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticles in solids. However, little is known about the level repulsion when more than two quasiparticles are present; for example, in a strongly interacting quantum system where a quasiparticle can spontaneously decay into a many-particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. In our fine-resolution neutron spectroscopy study of magnetic quasiparticles in the frustrated quantum magnet BiCu2PO6, we observe a renormalization of the quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states.
Double-layer shocks in a magnetized quantum plasma
Misra, A. P.; Samanta, S.
2010-09-15
The formation of small but finite amplitude electrostatic shocks in the propagation of quantum ion-acoustic waves obliquely to an external magnetic field is reported in a quantum electron-positron-ion plasma. Such shocks are seen to have double-layer (DL) structures composed of the compressive and accompanying rarefactive slow-wave fronts. Existence of such DL shocks depends critically on the quantum coupling parameter H associated with the Bohm potential and the positron to electron density ratio {delta}. The profiles may, however, steepen initially and reach a steady state with a number of solitary waves in front of the shocks. Such novel DL shocks could be a good candidate for particle acceleration in intense laser-solid density plasma interaction experiments as well as in compact astrophysical objects, e.g., magnetized white dwarfs.
FIT-MART: Quantum Magnetism with a Gentle Learning Curve
NASA Astrophysics Data System (ADS)
Engelhardt, Larry; Garland, Scott C.; Rainey, Cameron; Freeman, Ray A.
We present a new open-source software package, FIT-MART, that allows non-experts to quickly get started sim- ulating quantum magnetism. FIT-MART can be downloaded as a platform-idependent executable Java (JAR) file. It allows the user to define (Heisenberg) Hamiltonians by electronically drawing pictures that represent quantum spins and operators. Sliders are automatically generated to control the values of the parameters in the model, and when the values change, several plots are updated in real time to display both the resulting energy spectra and the equilibruim magnetic properties. Several experimental data sets for real magnetic molecules are included in FIT-MART to allow easy comparison between simulated and experimental data, and FIT-MART users can also import their own data for analysis and compare the goodness of fit for different models.
Theory of the thermal Hall effect in quantum magnets.
Katsura, Hosho; Nagaosa, Naoto; Lee, Patrick A
2010-02-12
We present a theory of the thermal Hall effect in insulating quantum magnets, where the heat current is totally carried by charge-neutral objects such as magnons and spinons. Two distinct types of thermal Hall responses are identified. For ordered magnets, the intrinsic thermal Hall effect for magnons arises when certain conditions are satisfied for the lattice geometry and the underlying magnetic order. The other type is allowed in a spin liquid which is a novel quantum state since there is no order even at zero temperature. For this case, the deconfined spinons contribute to the thermal Hall response due to Lorentz force. These results offer a clear experimental method to prove the existence of the deconfined spinons via a thermal transport phenomenon.
Frustrated quantum magnetism in the 6H-perovskites
NASA Astrophysics Data System (ADS)
Quilliam, Jeffrey
I will review the recent state of research on the 6H-perovskites, Ba3MA2O9, a large class of materials that can accommodate many different magnetic ions on ostensibly triangular lattices. This class of materials has given rise to several important discoveries in recent years, including quantum spin liquids, a quantum spin-orbital liquid and the first perfectly triangular spin-1/2 antiferromagnet. Many of these materials also provide an interesting interplay of magnetic, orbital and charge degrees of freedom. Others suffer from high levels of site disorder, which leads to interesting physics, at least in the case of the spin-orbital liquid candidate Ba3CuSb2O9. I will primarily discuss our recent work on the materials Ba3MSb2O9, where M = Cu, Ni and Co using the techniques of nuclear magnetic resonance (NMR), muon spin rotation (μSR) and ultrasound velocity measurements.
Quantum theory of spin alignment in a circular magnetic nanotube
NASA Astrophysics Data System (ADS)
Bergmann, Gerd; Thompson, Richard S.; Lu, Jia G.
2015-12-01
When electron spin and momentum couple in a solid, one generally obtains intriguing and unexpected phenomena. Metallic ferromagnetic nanotubes of cobalt with circular magnetization, which have been prepared by us and others, are a particularly interesting system. Here the spins of the conduction electrons are frustrated. They would like to align parallel to the magnetic field of the magnetization, but as the electrons move quickly around the tube the spins cannot follow the magnetization direction. In a previous short theoretical paper we solved the spin dynamics using a classical model. Here we generalize our work to a quantum mechanical model. The surprising result is that the spin of most conduction electrons is not parallel or anti-parallel to the circumferential magnetization but mostly parallel or anti-parallel to the axis of the nanotube. This result means that such a cobalt nanotube is a different ferromagnet from a cobalt film or bulk cobalt.
Magnetic resonance force microscopy and a solid state quantum computer.
Pelekhov, D. V.; Martin, I.; Suter, A.; Reagor, D. W.; Hammel, P. C.
2001-01-01
A Quantum Computer (QC) is a device that utilizes the principles of Quantum Mechanics to perform computations. Such a machine would be capable of accomplishing tasks not achievable by means of any conventional digital computer, for instance factoring large numbers. Currently it appears that the QC architecture based on an array of spin quantum bits (qubits) embedded in a solid-state matrix is one of the most promising approaches to fabrication of a scalable QC. However, the fabrication and operation of a Solid State Quantum Computer (SSQC) presents very formidable challenges; primary amongst these are: (1) the characterization and control of the fabrication process of the device during its construction and (2) the readout of the computational result. Magnetic Resonance Force Microscopy (MRFM)--a novel scanning probe technique based on mechanical detection of magnetic resonance-provides an attractive means of addressing these requirements. The sensitivity of the MRFM significantly exceeds that of conventional magnetic resonance measurement methods, and it has the potential for single electron spin detection. Moreover, the MRFM is capable of true 3D subsurface imaging. These features will make MRFM an invaluable tool for the implementation of a spin-based QC. Here we present the general principles of MRFM operation, the current status of its development and indicate future directions for its improvement.
NMR profiling of quantum electron solids in high magnetic fields
NASA Astrophysics Data System (ADS)
Tiemann, L.; Rhone, T. D.; Shibata, N.; Muraki, K.
2014-09-01
When the motion of electrons is restricted to a plane under a perpendicular magnetic field, a variety of quantum phases emerge at low temperatures, the properties of which are dictated by the Coulomb interaction and its interplay with disorder. At very strong magnetic field, the sequence of fractional quantum Hall liquid phases terminates in an insulating phase, which is widely believed to be due to the solidification of electrons into domains possessing Wigner crystal order. The existence of such Wigner crystal domains is signalled by the emergence of microwave pinning-mode resonances, which reflect the mechanical properties characteristic of a solid. However, the most direct manifestation of the broken translational symmetry accompanying the solidification--the spatial modulation of particles' probability amplitudes--has not been observed yet. Here, we demonstrate that nuclear magnetic resonance provides a direct probe of the density topography of electron solids in the integer and fractional quantum Hall regimes. The data uncover quantum and thermal fluctuations of lattice electrons resolved on the nanometre scale. Our results pave the way to studies of other exotic phases with non-trivial spatial spin/charge order.
Ferroelectricity by Bose–Einstein condensation in a quantum magnet
Kimura, S.; Kakihata, K.; Sawada, Y.; Watanabe, K.; Matsumoto, M.; Hagiwara, M.; Tanaka, H.
2016-01-01
The Bose–Einstein condensation is a fascinating phenomenon, which results from quantum statistics for identical particles with an integer spin. Surprising properties, such as superfluidity, vortex quantization or Josephson effect, appear owing to the macroscopic quantum coherence, which spontaneously develops in Bose–Einstein condensates. Realization of Bose–Einstein condensation is not restricted in fluids like liquid helium, a superconducting phase of paired electrons in a metal and laser-cooled dilute alkali atoms. Bosonic quasi-particles like exciton-polariton and magnon in solids-state systems can also undergo Bose–Einstein condensation in certain conditions. Here, we report that the quantum coherence in Bose–Einstein condensate of the magnon quasi particles yields spontaneous electric polarization in the quantum magnet TlCuCl3, leading to remarkable magnetoelectric effect. Very soft ferroelectricity is realized as a consequence of the O(2) symmetry breaking by magnon Bose–Einstein condensation. The finding of this ferroelectricity will open a new window to explore multi-functionality of quantum magnets. PMID:27666875
Tailoring Magnetism in Bulk Semiconductors and Quantum Dots
NASA Astrophysics Data System (ADS)
Zutic, Igor
2008-03-01
Carrier-mediated magnetism in semiconductors shows important and potentially useful differences from their metallic counterparts [1]. For example, in magnetically doped semiconductors the change in carrier density induced by light or bias could be sufficient to turn the ferromagnetism on and off. However, there remain many important challenges to fully understand these materials. Our density functional theory study of Mn- doped II-IV-V2 chalcopyrites [2] reveals that variation of magnetic properties across 64 different materials cannot be explained by the dominant models of ferromagnetism in semiconductors. We observe no qualitative similarity with the suggested Curie temperature scaling with the inverse cube of the lattice constant [3]. In contrast to most of the theoretical studies, we explicitly include the temperature dependence of the carrier density and propose a model which permits analysis of the thermodynamic stability of the competing magnetic states [4]. As an example we analyze the stability of a possible reentrant ferromagnetic semiconductor and discuss the experimental support for this prediction. An increasing temperature leads to an increased carrier density such that the enhanced coupling between magnetic impurities results in the onset of ferromagnetism as temperature is raised. We also use the real space finite-temperature local spin density approximation to examine magnetically doped quantum dots in which the interplay of quantum confinement and strong Coulomb interactions can lead to novel possibilities to tailor magnetism. We reveal that, even at a fixed number of carriers, the gate induced changes in the screening [5] or deviations from isotropic quantum confinement [6] could allow for a reversible control of magnetism and switching between zero and finite magnetization. Such magnetic quantum dots could also provide versatile voltage-control of spin currents and spin filtering. The work done in collaboration with S. C. Erwin (Naval Research
Quantum anomalous Hall effect in magnetic topological insulators
Wang, Jing; Lian, Biao; Zhang, Shou -Cheng
2015-08-25
The search for topologically non-trivial states of matter has become an important goal for condensed matter physics. Here, we give a theoretical introduction to the quantum anomalous Hall (QAH) effect based on magnetic topological insulators in two-dimensions (2D) and three-dimensions (3D). In 2D topological insulators, magnetic order breaks the symmetry between the counter-propagating helical edge states, and as a result, the quantum spin Hall effect can evolve into the QAH effect. In 3D, magnetic order opens up a gap for the topological surface states, and chiral edge state has been predicted to exist on the magnetic domain walls. We presentmore » the phase diagram in thin films of a magnetic topological insulator and review the basic mechanism of ferromagnetic order in magnetically doped topological insulators. We also review the recent experimental observation of the QAH effect. Furthermore, we discuss more recent theoretical work on the coexistence of the helical and chiral edge states, multi-channel chiral edge states, the theory of the plateau transition, and the thickness dependence in the QAH effect.« less
Quantum anomalous Hall effect in magnetic topological insulators
Wang, Jing; Lian, Biao; Zhang, Shou -Cheng
2015-08-25
The search for topologically non-trivial states of matter has become an important goal for condensed matter physics. Here, we give a theoretical introduction to the quantum anomalous Hall (QAH) effect based on magnetic topological insulators in two-dimensions (2D) and three-dimensions (3D). In 2D topological insulators, magnetic order breaks the symmetry between the counter-propagating helical edge states, and as a result, the quantum spin Hall effect can evolve into the QAH effect. In 3D, magnetic order opens up a gap for the topological surface states, and chiral edge state has been predicted to exist on the magnetic domain walls. We present the phase diagram in thin films of a magnetic topological insulator and review the basic mechanism of ferromagnetic order in magnetically doped topological insulators. We also review the recent experimental observation of the QAH effect. Furthermore, we discuss more recent theoretical work on the coexistence of the helical and chiral edge states, multi-channel chiral edge states, the theory of the plateau transition, and the thickness dependence in the QAH effect.
Yamazoe, M; Kato, T; Suzuki, K; Adachi, M; Shibayama, A; Hoshi, K; Itou, M; Tsuji, N; Sakurai, Y; Sakurai, H
2016-11-01
Spin selective magnetic hysteresis (SSMH) curves, orbital selective magnetic hysteresis (OSMH) curves and magnetic quantum number selective SSMH curves are obtained for CoFeB/MgO multilayer films by combining magnetic Compton profile measurements and superconducting quantum interference device (SQUID) magnetometer measurements. Although the SQUID magnetometer measurements do not show perpendicular magnetic anisotropy (PMA) in the CoFeB/MgO multilayer film, PMA behavior is observed in the OSMH and SSMH curves for the |m| = 2 magnetic quantum number states. These facts indicate that magnetization switching behavior is dominated by the orbital magnetization of the |m| = 2 magnetic quantum number states. PMID:27602698
NASA Astrophysics Data System (ADS)
Yamazoe, M.; Kato, T.; Suzuki, K.; Adachi, M.; Shibayama, A.; Hoshi, K.; Itou, M.; Tsuji, N.; Sakurai, Y.; Sakurai, H.
2016-11-01
Spin selective magnetic hysteresis (SSMH) curves, orbital selective magnetic hysteresis (OSMH) curves and magnetic quantum number selective SSMH curves are obtained for CoFeB/MgO multilayer films by combining magnetic Compton profile measurements and superconducting quantum interference device (SQUID) magnetometer measurements. Although the SQUID magnetometer measurements do not show perpendicular magnetic anisotropy (PMA) in the CoFeB/MgO multilayer film, PMA behavior is observed in the OSMH and SSMH curves for the |m| = 2 magnetic quantum number states. These facts indicate that magnetization switching behavior is dominated by the orbital magnetization of the |m| = 2 magnetic quantum number states.
Awschalom, D.D.; Crooker, S.A.; Lyo, S.K.; Rickel, D.G.; Samarth, N.
1999-05-24
Magnetic semiconductors offer a unique possibility for strongly tuning the intrinsic alloy disorder potential with applied magnetic field. We report the direct observation of a series of step-like reductions in the magnetic alloy disorder potential in single ZnSe/Zn(Cd,Mn)Se quantum wells between O and 60 Tesla. This disorder, measured through the linewidth of low temperature photoluminescence spectra drops abruptly at -19, 36, and 53 Tesla, in concert with observed magnetization steps. Conventional models of alloy disorder (developed for nonmagnetic semiconductors) reproduce the general shape of the data, but markedly underestimate the size of the linewidth reduction.
Surface Induced Magnetism in Quantum Dots
Meulenberg, R W; Lee, J I
2009-08-20
The study of nanometer sized semiconductor crystallites, also known as quantum dots (QDs), has seen rapid advancements in recent years in scientific disciplines ranging from chemistry, physics, biology, materials science, and engineering. QD materials of CdSe, ZnSe, InP, as well as many others, can be prepared in the size range of 1-10 nm producing uniform, nearly monodisperse materials that are typically coated with organic molecules [1-3]. The strength of charge carrier confinement, which dictates the size-dependent properties, in these QDs depends on the nature of the material and can be correlated to the Bohr radius for the system of interest. For instance, the Bohr radius for CdSe is {approx} 5 nm, while in the more covalent structure of InP, the Bohr radius approaches {approx} 10 nm. The study of CdSe QDs has been particularly extensive during the last decade because they exhibit unique and tunable optical properties and are readily synthesized with high-crystallinity and narrow size dispersions. Although the core electronic properties of CdSe are explained in terms of the quantum confinement model, experimental efforts to elucidate the surface structure of these materials have been limited. Typically, colloidal CdSe QDs are coated with an organic surfactant, which typically consists of an organo-phosphine, -thiol, or -amine, that has the function of energetically relaxing defect states via coordination to partially coordinated surface atoms. The organic surfactant also acts to enhance carrier confinement and prevent agglomeration of the particles. Chemically, it has been shown that the bonding of the surfactant to the CdSe QD occurs through Cd atoms resulting cleavage of the Se atoms and formation of a Cd-rich (i.e. non-stoichiometric) particle [5].
Current-driven spin dynamics of artificially constructed quantum magnets.
Khajetoorians, Alexander Ako; Baxevanis, Benjamin; Hübner, Christoph; Schlenk, Tobias; Krause, Stefan; Wehling, Tim Oliver; Lounis, Samir; Lichtenstein, Alexander; Pfannkuche, Daniela; Wiebe, Jens; Wiesendanger, Roland
2013-01-01
The future of nanoscale spin-based technologies hinges on a fundamental understanding and dynamic control of atomic-scale magnets. The role of the substrate conduction electrons on the dynamics of supported atomic magnets is still a question of interest lacking experimental insight. We characterized the temperature-dependent dynamical response of artificially constructed magnets, composed of a few exchange-coupled atomic spins adsorbed on a metallic substrate, to spin-polarized currents driven and read out by a magnetic scanning tunneling microscope tip. The dynamics, reflected by two-state spin noise, is quantified by a model that considers the interplay between quantum tunneling and sequential spin transitions driven by electron spin-flip processes and accounts for an observed spin-transfer torque effect.
Distributed Hybridization Model for Quantum Critical Behavior in Magnetic Quasicrystals
NASA Astrophysics Data System (ADS)
Otsuki, Junya; Kusunose, Hiroaki
2016-07-01
A quantum critical behavior of the magnetic susceptibility was observed in a quasicrystal containing ytterbium. At the same time, a mixed-valence feature of Yb ions was reported, which appears to be incompatible with the magnetic instability. We derive the magnetic susceptibility by expressing the quasiperiodicity as the distributed hybridization strength between Yb 4f and conduction electrons. Assuming a wide distribution of the hybridization strength, the most f electrons behave as renormalized paramagnetic states in the Kondo or mixed-valence regime, but a small number of f moments remain unscreened. As a result, the bulk magnetic susceptibility exhibits a nontrivial power-law-like behavior, while the average f-electron occupation is that of mixed-valence systems. This model thus resolves two contradictory properties of Yb quasicrystals.
Uniform Doping in Quantum-Dots-Based Dilute Magnetic Semiconductor.
Saha, Avijit; Shetty, Amitha; Pavan, A R; Chattopadhyay, Soma; Shibata, Tomohiro; Viswanatha, Ranjani
2016-07-01
Effective manipulation of magnetic spin within a semiconductor leading to a search for ferromagnets with semiconducting properties has evolved into an important field of dilute magnetic semiconductors (DMS). Although a lot of research is focused on understanding the still controversial origin of magnetism, efforts are also underway to develop new materials with higher magnetic temperatures for spintronics applications. However, so far, efforts toward quantum-dots(QDs)-based DMS materials are plagued with problems of phase separation, leading to nonuniform distribution of dopant ions. In this work, we have developed a strategy to synthesize highly crystalline, single-domain DMS system starting from a small magnetic core and allowing it to diffuse uniformly inside a thick CdS semiconductor matrix and achieve DMS QDs. X-ray absorption fine structure (XAFS) spectroscopy and energy-dispersive X-ray spectroscopy-scanning transmission electron microscopy (STEM-EDX) indicates the homogeneous distribution of magnetic impurities inside the semiconductor QDs leading to superior magnetic property. Further, the versatility of this technique was demonstrated by obtaining ultra large particles (∼60 nm) with uniform doping concentration as well as demonstrating the high quality magnetic response. PMID:27295453
Uniform Doping in Quantum-Dots-Based Dilute Magnetic Semiconductor.
Saha, Avijit; Shetty, Amitha; Pavan, A R; Chattopadhyay, Soma; Shibata, Tomohiro; Viswanatha, Ranjani
2016-07-01
Effective manipulation of magnetic spin within a semiconductor leading to a search for ferromagnets with semiconducting properties has evolved into an important field of dilute magnetic semiconductors (DMS). Although a lot of research is focused on understanding the still controversial origin of magnetism, efforts are also underway to develop new materials with higher magnetic temperatures for spintronics applications. However, so far, efforts toward quantum-dots(QDs)-based DMS materials are plagued with problems of phase separation, leading to nonuniform distribution of dopant ions. In this work, we have developed a strategy to synthesize highly crystalline, single-domain DMS system starting from a small magnetic core and allowing it to diffuse uniformly inside a thick CdS semiconductor matrix and achieve DMS QDs. X-ray absorption fine structure (XAFS) spectroscopy and energy-dispersive X-ray spectroscopy-scanning transmission electron microscopy (STEM-EDX) indicates the homogeneous distribution of magnetic impurities inside the semiconductor QDs leading to superior magnetic property. Further, the versatility of this technique was demonstrated by obtaining ultra large particles (∼60 nm) with uniform doping concentration as well as demonstrating the high quality magnetic response.
Thermal and magnetic quantum discord in Heisenberg models
Werlang, T.; Rigolin, Gustavo
2010-04-15
We investigate how quantum correlations [quantum discord (QD)] of a two-qubit one-dimensional XYZ Heisenberg chain in thermal equilibrium depend on the temperature T of the bath and also on an external magnetic field B. We show that the behavior of thermal QD differs in many unexpected ways from thermal entanglement. For example, we show situations where QD increases with T when entanglement decreases, cases where QD increases with T even in regions with zero entanglement, and that QD signals a quantum phase transition even at finite T. We also show that by properly tuning B or the interaction between the qubits we get nonzero QD for any T and we present an effect not seen for entanglement, the 'regrowth' of thermal QD.
Quantum corrections crossover and ferromagnetism in magnetic topological insulators.
Bao, Lihong; Wang, Weiyi; Meyer, Nicholas; Liu, Yanwen; Zhang, Cheng; Wang, Kai; Ai, Ping; Xiu, Faxian
2013-01-01
Revelation of emerging exotic states of topological insulators (TIs) for future quantum computing applications relies on breaking time-reversal symmetry and opening a surface energy gap. Here, we report on the transport response of Bi2Te3 TI thin films in the presence of varying Cr dopants. By tracking the magnetoconductance (MC) in a low doping regime we observed a progressive crossover from weak antilocalization (WAL) to weak localization (WL) as the Cr concentration increases. In a high doping regime, however, increasing Cr concentration yields a monotonically enhanced anomalous Hall effect (AHE) accompanied by an increasing carrier density. Our results demonstrate a possibility of manipulating bulk ferromagnetism and quantum transport in magnetic TI, thus providing an alternative way for experimentally realizing exotic quantum states required by spintronic applications.
Quantum synchrotron spectra from semirelativistic electrons in teragauss magnetic fields
NASA Technical Reports Server (NTRS)
Brainerd, J. J.
1987-01-01
Synchrotron spectra are calculated from quantum electrodynamic transition rates for thermal and power-law electron distributions. It is shown that quantum effects appear in thermal spectra when the photon energy is greater than the electron temperature, and in power-law spectra when the electron energy in units of the electron rest mass times the magnetic field strength in units of the critical field strength is of order unity. These spectra are compared with spectra calculated from the ultrarelativistic approximation for synchrotron emission. It is found that the approximation for the power-law spectra is good, and the approximation for thermal spectra produces the shape of the spectrum accurately but fails to give the correct normalization. Single photon pair creation masks the quantum effects for power-law distributions, so only modifications to thermal spectra are important for gamma-ray bursts.
Quantum Corrections Crossover and Ferromagnetism in Magnetic Topological Insulators
Bao, Lihong; Wang, Weiyi; Meyer, Nicholas; Liu, Yanwen; Zhang, Cheng; Wang, Kai; Ai, Ping; Xiu, Faxian
2013-01-01
Revelation of emerging exotic states of topological insulators (TIs) for future quantum computing applications relies on breaking time-reversal symmetry and opening a surface energy gap. Here, we report on the transport response of Bi2Te3 TI thin films in the presence of varying Cr dopants. By tracking the magnetoconductance (MC) in a low doping regime we observed a progressive crossover from weak antilocalization (WAL) to weak localization (WL) as the Cr concentration increases. In a high doping regime, however, increasing Cr concentration yields a monotonically enhanced anomalous Hall effect (AHE) accompanied by an increasing carrier density. Our results demonstrate a possibility of manipulating bulk ferromagnetism and quantum transport in magnetic TI, thus providing an alternative way for experimentally realizing exotic quantum states required by spintronic applications. PMID:23928713
NASA Astrophysics Data System (ADS)
Demić, Aleksandar; Radovanović, Jelena; Milanović, Vitomir
2016-08-01
We present a method for modeling nonparabolicity effects (NPE) in quantum nanostructures in presence of external electric and magnetic field by using second order perturbation theory. The method is applied to analysis of quantum well structure and active region of a quantum cascade laser (QCL). This model will allow us to examine the influence of magnetic field on dipole matrix element in QCL structures, which will provide a better insight to how NPE can affect the gain of QCL structures.
Crystallization in Ising quantum magnets and Rydberg superatoms
NASA Astrophysics Data System (ADS)
Schauss, Peter
2016-05-01
Dominating finite-range interactions in many-body systems can lead to intriguing self-ordered phases of matter. For quantum magnets, Ising models with power-law interactions are among the most elementary systems that support such phases. These models can be implemented by laser coupling ensembles of ultracold atoms to Rydberg states. In this talk, I will report on the experimental preparation of crystalline ground states of such spin systems. We observe a magnetization staircase as a function of the system size and show directly the emergence of crystalline states with vanishing susceptibility. Recent results connect these findings with the picture of Rydberg superatoms. We investigated their scalability and observed collective Rabi oscillations with the perspective of using Rydberg superatoms as collective qubits. Experiments performed at Max-Planck Institute of Quantum Optics, Garching, Germany.
Magnetism in Parent Iron Chalcogenides: Quantum Fluctuations Select Plaquette Order
NASA Astrophysics Data System (ADS)
Ducatman, Samuel; Perkins, Natalia B.; Chubukov, Andrey
2012-10-01
We analyze magnetic order in Fe chalcogenide Fe1+yTe, the parent compound of the high-temperature superconductor Fe1+yTe1-xSex. Experiments show that magnetic order in this material contains components with momentum Q1=(π/2,π/2) and Q2=(π/2,-π/2) in the Fe only Brillouin zone. The actual spin order depends on the interplay between these two components. Previous works assumed that the ordered state has a single Q (either Q1 or Q2). In such a state, spins form double stripes along one of the diagonals breaking the rotational C4 symmetry. We show that quantum fluctuations actually select another order—a double Q plaquette state with equal weight of Q1 and Q2 components, which preserves C4 symmetry. We argue that the order in Fe1+yTe is determined by the competition between quantum fluctuations and magnetoelastic coupling.
Quantum mechanism of nonlocal Gilbert damping in magnetic trilayers
NASA Astrophysics Data System (ADS)
Barati, Ehsan; Cinal, Marek
2015-06-01
A fully quantum-mechanical calculation of the Gilbert damping constant α in magnetic trilayers is done by employing the torque-correlation formula within a realistic tight-binding model. A remarkable enhancement of α in Co/NM1/NM2 trilayers is obtained due to adding the caps NM2=Pd, Pt, and it decays with the thickness of the spacers NM1=Cu, Ag, Au in agreement with experiment. Nonlocal origin of the Gilbert damping is visualized with its atomic layer contributions. It is shown that magnetization in Co is damped remotely by strong spin-orbit coupling in NM2 via quantum states with large amplitude in both Co and NM2.
Designing frustrated quantum magnets with laser-dressed Rydberg atoms.
Glaetzle, Alexander W; Dalmonte, Marcello; Nath, Rejish; Gross, Christian; Bloch, Immanuel; Zoller, Peter
2015-05-01
We show how a broad class of lattice spin-1/2 models with angular- and distance-dependent couplings can be realized with cold alkali atoms stored in optical or magnetic trap arrays. The effective spin-1/2 is represented by a pair of atomic ground states, and spin-spin interactions are obtained by admixing van der Waals interactions between fine-structure split Rydberg states with laser light. The strengths of the diagonal spin interactions as well as the "flip-flop," and "flip-flip" and "flop-flop" interactions can be tuned by exploiting quantum interference, thus realizing different spin symmetries. The resulting energy scales of interactions compare well with typical temperatures and decoherence time scales, making the exploration of exotic forms of quantum magnetism, including emergent gauge theories and compass models, accessible within state-of-the-art experiments.
Designing Frustrated Quantum Magnets with Laser-Dressed Rydberg Atoms
NASA Astrophysics Data System (ADS)
Glaetzle, Alexander W.; Dalmonte, Marcello; Nath, Rejish; Gross, Christian; Bloch, Immanuel; Zoller, Peter
2015-05-01
We show how a broad class of lattice spin-1 /2 models with angular- and distance-dependent couplings can be realized with cold alkali atoms stored in optical or magnetic trap arrays. The effective spin-1 /2 is represented by a pair of atomic ground states, and spin-spin interactions are obtained by admixing van der Waals interactions between fine-structure split Rydberg states with laser light. The strengths of the diagonal spin interactions as well as the "flip-flop," and "flip-flip" and "flop-flop" interactions can be tuned by exploiting quantum interference, thus realizing different spin symmetries. The resulting energy scales of interactions compare well with typical temperatures and decoherence time scales, making the exploration of exotic forms of quantum magnetism, including emergent gauge theories and compass models, accessible within state-of-the-art experiments.
Designing frustrated quantum magnets with laser-dressed Rydberg atoms.
Glaetzle, Alexander W; Dalmonte, Marcello; Nath, Rejish; Gross, Christian; Bloch, Immanuel; Zoller, Peter
2015-05-01
We show how a broad class of lattice spin-1/2 models with angular- and distance-dependent couplings can be realized with cold alkali atoms stored in optical or magnetic trap arrays. The effective spin-1/2 is represented by a pair of atomic ground states, and spin-spin interactions are obtained by admixing van der Waals interactions between fine-structure split Rydberg states with laser light. The strengths of the diagonal spin interactions as well as the "flip-flop," and "flip-flip" and "flop-flop" interactions can be tuned by exploiting quantum interference, thus realizing different spin symmetries. The resulting energy scales of interactions compare well with typical temperatures and decoherence time scales, making the exploration of exotic forms of quantum magnetism, including emergent gauge theories and compass models, accessible within state-of-the-art experiments. PMID:25978228
Quantum transport in magnetic topological insulator thin films.
Lu, Hai-Zhou; Zhao, An; Shen, Shun-Qing
2013-10-01
The experimental observation of the long-sought quantum anomalous Hall effect was recently reported in magnetically doped topological insulator thin films [Chang et al., Science 340, 167 (2013)]. An intriguing observation is a rapid decrease from the quantized plateau in the Hall conductance, accompanied by a peak in the longitudinal conductance as a function of the gate voltage. Here, we present a quantum transport theory with an effective model for magnetic topological insulator thin films. The good agreement between theory and experiment reveals that the measured transport originates from a topologically nontrivial conduction band which, near its band edge, has concentrated Berry curvature and a local maximum in group velocity. The indispensable roles of the broken structure inversion and particle-hole symmetries are also revealed. The results are instructive for future experiments and transport studies based on first-principles calculations.
Design of magnetic coordination complexes for quantum computing.
Aromí, Guillem; Aguilà, David; Gamez, Patrick; Luis, Fernando; Roubeau, Olivier
2012-01-21
A very exciting prospect in coordination chemistry is to manipulate spins within magnetic complexes for the realization of quantum logic operations. An introduction to the requirements for a paramagnetic molecule to act as a 2-qubit quantum gate is provided in this tutorial review. We propose synthetic methods aimed at accessing such type of functional molecules, based on ligand design and inorganic synthesis. Two strategies are presented: (i) the first consists in targeting molecules containing a pair of well-defined and weakly coupled paramagnetic metal aggregates, each acting as a carrier of one potential qubit, (ii) the second is the design of dinuclear complexes of anisotropic metal ions, exhibiting dissimilar environments and feeble magnetic coupling. The first systems obtained from this synthetic program are presented here and their properties are discussed.
Two-Electron Spherical Quantum Dot in a Magnetic Field
NASA Astrophysics Data System (ADS)
Poszwa, A.
2016-07-01
We investigate three-dimensional, two-electron quantum dots in an external magnetic field B. Due to mixed spherical and cylindrical symmetry the Schrödinger equation is not completely separable. Highly accurate numerical solutions, for a wide range of B, have been obtained by the expansion of wavefunctions in double-power series and by imposing on the radial functions appropriate boundary conditions. The asymptotic limit of a very strong magnetic field and the 2D approach have been considered. Ground state properties of the two-electron semiconductor quantum dots are investigated using both the 3D and 2D models. Theoretical calculations have been compared with recent experimental results.
Exchange interaction effects on waves in magnetized quantum plasmas
Trukhanova, Mariya Iv. Andreev, Pavel A.
2015-02-15
We have applied the many-particle quantum hydrodynamics that includes the Coulomb exchange interaction to magnetized quantum plasmas. We considered a number of wave phenomena that are affected by the Coulomb exchange interaction. Since the Coulomb exchange interaction affects the longitudinal and transverse-longitudinal waves, we focused our attention on the Langmuir waves, the Trivelpiece-Gould waves, the ion-acoustic waves in non-isothermal magnetized plasmas, the dispersion of the longitudinal low-frequency ion-acoustic waves, and low-frequency electromagnetic waves at T{sub e} ≫ T{sub i}. We have studied the dispersion of these waves and present the numeric simulation of their dispersion properties.
Quantum Mechanics with a Momentum-Space Artificial Magnetic Field
NASA Astrophysics Data System (ADS)
Price, Hannah M.; Ozawa, Tomoki; Carusotto, Iacopo
2014-11-01
The Berry curvature is a geometrical property of an energy band which acts as a momentum space magnetic field in the effective Hamiltonian describing single-particle quantum dynamics. We show how this perspective may be exploited to study systems directly relevant to ultracold gases and photonics. Given the exchanged roles of momentum and position, we demonstrate that the global topology of momentum space is crucially important. We propose an experiment to study the Harper-Hofstadter Hamiltonian with a harmonic trap that will illustrate the advantages of this approach and that will also constitute the first realization of magnetism on a torus.
Quantum ignition of deflagration in the Fe8 molecular magnet
NASA Astrophysics Data System (ADS)
Leviant, Tom; Keren, Amit; Zeldov, Eli; Myasoedov, Yuri
2014-10-01
We report spatially resolved, time-dependent, magnetization reversal measurements of an Fe8 single molecular magnet using a microscopic Hall bar array. We found that a deflagration process, where molecules reverse their spin direction along a moving front, can be ignited quantum mechanically (T →0) at a resonance field, with no phonon pulse. The avalanche front velocity is of the order of 1m/s and is sensitive to field gradients and sweep rates. We also measured the thermal diffusivity κ in Fe8. This allows us to estimate the "flame" temperature.
Single cell magnetic imaging using a quantum diamond microscope
Park, H.; Weissleder, R.; Yacoby, A.; Lukin, M. D.; Lee, H.; Walsworth, R. L.; Connolly, C. B.
2015-01-01
We apply a quantum diamond microscope to detection and imaging of immunomagnetically labeled cells. This instrument uses nitrogen-vacancy (NV) centers in diamond for correlated magnetic and fluorescence imaging. Our device provides single-cell resolution and two orders of magnitude larger field of view (~1 mm2) than previous NV imaging technologies, enabling practical applications. To illustrate, we quantify cancer biomarkers expressed by rare tumor cells in a large population of healthy cells. PMID:26098019
Single-cell magnetic imaging using a quantum diamond microscope.
Glenn, David R; Lee, Kyungheon; Park, Hongkun; Weissleder, Ralph; Yacoby, Amir; Lukin, Mikhail D; Lee, Hakho; Walsworth, Ronald L; Connolly, Colin B
2015-08-01
We apply a quantum diamond microscope for detection and imaging of immunomagnetically labeled cells. This instrument uses nitrogen-vacancy (NV) centers in diamond for correlated magnetic and fluorescence imaging. Our device provides single-cell resolution and a field of view (∼1 mm(2)) two orders of magnitude larger than that of previous NV imaging technologies, enabling practical applications. To illustrate, we quantified cancer biomarkers expressed by rare tumor cells in a large population of healthy cells.
Superconductivity of the magnetized electron gas of a quantum cylinder
Eminov, P. A. Sezonov, Yu. I.
2008-10-15
A microscopic theory of superconductivity is developed for the magnetized electron gas on a cylindrical surface. The Gibbs free energy is calculated for the superconducting system. A gap equation is derived that determines the critical temperature as a function of the quantum-cylinder dimensions and the Aharonov-Bohm parameter. It is shown that the gap not only exhibits Aharonov-Bohm oscillations, but also oscillates with varying curvature of the cylindrical surface.
Exact Results in Frustrated Quantum Magnetism
NASA Astrophysics Data System (ADS)
Miyahara, Shin
Most of the exact results in frustrated spin systems have for a long time been regarded as of purely academic interest, being realized only due to the special geometry of the lattices concerned. However, recent developments in material design offer the genuine possibility of producing such exact states in real materials. In fact, the exact dimer singlet state of the two-dimensional Shastry-Sutherland model has already been found as the ground state of the quasi-two-dimensional material SrCu2(BO3)2. The cooperation between experimentalists and theorists in investigating this material has caused rapid development in the understanding of low-dimensional frustrated spin systems in general, due to the extreme utility of cases where the ground state is known exactly. This fact provides information essential to recognizing novel magnetic behavior in external magnetic fields, at finite temperatures, and in other regimes. In this chapter, we introduce spin-1 / 2 models which have an exact ground state, considering first exactly solvable spin-1 / 2 Heisenberg models, exemplified by the sawtooth-chain model, the Majumdar-Ghosh model, the two-dimensional Shastry-Sutherland model, and a frustrated ladder model. Such exact states can be realized due to special symmetries on geometrically frustrated lattices. As a second class of examples, we introduce also some exact ground states in spin-1/2 models with multiple-spin interactions.
Role of the tuning parameter at magnetic quantum phase transitions
NASA Astrophysics Data System (ADS)
Fritsch, V.; Stockert, O.; Huang, C.-L.; Bagrets, N.; Kittler, W.; Taubenheim, C.; Pilawa, B.; Woitschach, S.; Huesges, Z.; Lucas, S.; Schneidewind, A.; Grube, K.; Löhneysen, H. v.
2015-07-01
Heavy-fermion systems, with their competition between Kondo and RKKY interactions, offer a rich variety of materials that may be driven to a magnetic quantum phase transition. Quite often, a quantum critical point can be approached by chemical substitution, notably of isoelectric ligands of Ce, as in CeCu6- x Au x and CePd1- x Ni x Al. While in the former we compare pressure and concentration tuning of the magnetic structure, the latter has the additional feature of geometric frustration due to the distorted kagomé sublattice of Ce atoms in the basal plane. We further present the system CeAu2Ge2 where minor structural differences between crystals grown from Sn or Au-Ge flux lead to pronounced differences in the magnetic structure, with several field-induced phases in samples grown from Au-Ge flux. Finally, non-isoelectronic substitution of Ti by V is studied in CeTi1- x V x Ge3 where CeTiGe3 is a ferromagnet, thus allowing the study of ferromagnetic quantum criticality, a rare case for heavy-fermion systems.
Magnetic and non-magnetic phases of a quantum spin liquid.
Pratt, F L; Baker, P J; Blundell, S J; Lancaster, T; Ohira-Kawamura, S; Baines, C; Shimizu, Y; Kanoda, K; Watanabe, I; Saito, G
2011-03-31
A quantum spin-liquid phase is an intriguing possibility for a system of strongly interacting magnetic units in which the usual magnetically ordered ground state is avoided owing to strong quantum fluctuations. It was first predicted theoretically for a triangular-lattice model with antiferromagnetically coupled S = 1/2 spins. Recently, materials have become available showing persuasive experimental evidence for such a state. Although many studies show that the ideal triangular lattice of S = 1/2 Heisenberg spins actually orders magnetically into a three-sublattice, non-collinear 120° arrangement, quantum fluctuations significantly reduce the size of the ordered moment. This residual ordering can be completely suppressed when higher-order ring-exchange magnetic interactions are significant, as found in nearly metallic Mott insulators. The layered molecular system κ-(BEDT-TTF)(2)Cu(2)(CN)(3) is a Mott insulator with an almost isotropic, triangular magnetic lattice of spin-1/2 BEDT-TTF dimers that provides a prime example of a spin liquid formed in this way. Despite a high-temperature exchange coupling, J, of 250 K (ref. 6), no obvious signature of conventional magnetic ordering is seen down to 20 mK (refs 7, 8). Here we show, using muon spin rotation, that applying a small magnetic field to this system produces a quantum phase transition between the spin-liquid phase and an antiferromagnetic phase with a strongly suppressed moment. This can be described as Bose-Einstein condensation of spin excitations with an extremely small spin gap. At higher fields, a second transition is found that suggests a threshold for deconfinement of the spin excitations. Our studies reveal the low-temperature magnetic phase diagram and enable us to measure characteristic critical properties. We compare our results closely with current theoretical models, and this gives some further insight into the nature of the spin-liquid phase.
Spin jam induced by quantum fluctuations in a frustrated magnet
Yang, Junjie; Samarakoon, Anjana; Dissanayake, Sachith; Ueda, Hiroaki; Klich, Israel; Iida, Kazuki; Pajerowski, Daniel; Butch, Nicholas P.; Huang, Q.; Copley, John R. D.; Lee, Seung-Hun
2015-01-01
Since the discovery of spin glasses in dilute magnetic systems, their study has been largely focused on understanding randomness and defects as the driving mechanism. The same paradigm has also been applied to explain glassy states found in dense frustrated systems. Recently, however, it has been theoretically suggested that different mechanisms, such as quantum fluctuations and topological features, may induce glassy states in defect-free spin systems, far from the conventional dilute limit. Here we report experimental evidence for existence of a glassy state, which we call a spin jam, in the vicinity of the clean limit of a frustrated magnet, which is insensitive to a low concentration of defects. We have studied the effect of impurities on SrCr9pGa12-9pO19 [SCGO(p)], a highly frustrated magnet, in which the magnetic Cr3+ (s = 3/2) ions form a quasi-2D triangular system of bipyramids. Our experimental data show that as the nonmagnetic Ga3+ impurity concentration is changed, there are two distinct phases of glassiness: an exotic glassy state, which we call a spin jam, for the high magnetic concentration region (p>0.8) and a cluster spin glass for lower magnetic concentration (p<0.8). This observation indicates that a spin jam is a unique vantage point from which the class of glassy states of dense frustrated magnets can be understood. PMID:26324917
Spin jam induced by quantum fluctuations in a frustrated magnet.
Yang, Junjie; Samarakoon, Anjana; Dissanayake, Sachith; Ueda, Hiroaki; Klich, Israel; Iida, Kazuki; Pajerowski, Daniel; Butch, Nicholas P; Huang, Q; Copley, John R D; Lee, Seung-Hun
2015-09-15
Since the discovery of spin glasses in dilute magnetic systems, their study has been largely focused on understanding randomness and defects as the driving mechanism. The same paradigm has also been applied to explain glassy states found in dense frustrated systems. Recently, however, it has been theoretically suggested that different mechanisms, such as quantum fluctuations and topological features, may induce glassy states in defect-free spin systems, far from the conventional dilute limit. Here we report experimental evidence for existence of a glassy state, which we call a spin jam, in the vicinity of the clean limit of a frustrated magnet, which is insensitive to a low concentration of defects. We have studied the effect of impurities on SrCr9pGa12-9pO19 [SCGO(p)], a highly frustrated magnet, in which the magnetic Cr(3+) (s = 3/2) ions form a quasi-2D triangular system of bipyramids. Our experimental data show that as the nonmagnetic Ga(3+) impurity concentration is changed, there are two distinct phases of glassiness: an exotic glassy state, which we call a spin jam, for the high magnetic concentration region (p > 0.8) and a cluster spin glass for lower magnetic concentration (p < 0.8). This observation indicates that a spin jam is a unique vantage point from which the class of glassy states of dense frustrated magnets can be understood.
Magnetic Field Assisted sub-THz Quantum Cascade Lasers
NASA Astrophysics Data System (ADS)
Wade, A.; Kim, Y.; Smirnov, D.; Kumar, S.; Hu, Q.; Williams, B. S.; Reno, J.
2009-03-01
In THz QCLs radiative transitions take place between closely-spaced 2D electronic subbands (1THz ˜ 4meV) of a multi-QW semiconductor system. THz quantum cascade lasers now cover the frequency range from 1.2 THz to 5 THz, though cryogenic cooling is still required. Further progress towards the realization of devices emitting at longer wavelengths (sub-THz QCLs) and higher temperatures may be realized in a system with additional lateral confinement. Here we use strong magnetic fields to achieve quasi-0D confinement in THz QCL based on the resonance phonon design. We studied two designs: (a) 2-well injector/2 well active region, emitting at 3 THz at B=0; and (b) 1-well injector/3-well active region, emitting at 2 THz at B=0 T. By applying the appropriate electrical bias and strong magnetic fields, we achieved laser emission at 0.8-0.9 THz at B>16 T [1], and 0.6 THz at B˜17 T, from devices a and b respectively. The ability to achieve sub-THz lasing is due to magnetic field enhanced population inversion in a quasi-0D QCL. [1] Wade, A et. al., Magnetic field assisted Terahertz quantum cascade laser operating up to 225K, Accepted for publication Nature Photonics (2009)
Atomic spin chains as testing ground for quantum magnetism
NASA Astrophysics Data System (ADS)
Otte, Sander
2015-03-01
The field of quantum magnetism aims to capture the rich emergent physics that arises when multiple spins interact, in terms of elementary models such as the spin 1/2 Heisenberg chain. Experimental platforms to verify these models are rare and generally do not provide the possibility to detect spin correlations locally. In my lab we use low-temperature scanning tunneling microscopy to design and build artificial spin lattices with atomic precision. Inelastic electron tunneling spectroscopy enables us to identify the ground state and probe spin excitations as a function of system size, location inside the lattice and coupling parameter values. Two types of collective excitations that play a role in many dynamic magnetic processes are spin waves (magnons) and spinons. Our experiments enable us to study both types of excitations. First, we have been able to map the standing spin wave modes of a ferromagnetic bit of six atoms, and to determine their role in the collective reversal process of the bit (Spinelli et al., Nature Materials 2014). More recently, we have crafted antiferromagnetic spin 1/2 XXZ chains, which allow us to observe spinon excitations, as well as the stepwise transition to a fully aligned phase beyond the critical magnetic field (Toskovic et al., in preparation). These findings create a promising experimental environment for putting quantum magnetic models to the test. Research funded by NWO and FOM.
Eslami, L. Faizabadi, E.
2014-05-28
The effect of magnetic contacts on spin-dependent electron transport and spin-accumulation in a quantum ring, which is threaded by a magnetic flux, is studied. The quantum ring is made up of four quantum dots, where two of them possess magnetic structure and other ones are subjected to the Rashba spin-orbit coupling. The magnetic quantum dots, referred to as magnetic quantum contacts, are connected to two external leads. Two different configurations of magnetic moments of the quantum contacts are considered; the parallel and the anti-parallel ones. When the magnetic moments are parallel, the degeneracy between the transmission coefficients of spin-up and spin-down electrons is lifted and the system can be adjusted to operate as a spin-filter. In addition, the accumulation of spin-up and spin-down electrons in non-magnetic quantum dots are different in the case of parallel magnetic moments. When the intra-dot Coulomb interaction is taken into account, we find that the electron interactions participate in separation between the accumulations of electrons with different spin directions in non-magnetic quantum dots. Furthermore, the spin-accumulation in non-magnetic quantum dots can be tuned in the both parallel and anti-parallel magnetic moments by adjusting the Rashba spin-orbit strength and the magnetic flux. Thus, the quantum ring with magnetic quantum contacts could be utilized to create tunable local magnetic moments which can be used in designing optimized nanodevices.
Pressure-induced transformations in molecular crystals
Taylor, R.D.; Hearne, G.R. |; Pasternak, M.P.
1995-09-01
A review is given on the unique features of the Moessbauer spectroscopy (MS) which by virtue of the quadrupole interaction and the lattice dynamics allows one to characterize some structural properties in the pressure-induced amorphous state of molecular crystals. Experiments were performed in GeI{sub 4}, SnI{sub 4} and SnBr{sub 4} by means of {sup 119}Sn and {sup 129}I MS with pressures to 35 GPa at cryogenic temperatures using diamond anvil cells.
Suzuki, Kosuke Takubo, Shota; Kato, Tadashi; Yamazoe, Masatoshi; Hoshi, Kazushi; Sakurai, Hiroshi; Homma, Yoshiya; Itou, Masayoshi; Sakurai, Yoshiharu
2014-08-18
A spin specific magnetic hysteresis (SSMH) curve and an orbital specific magnetic hysteresis (OSMH) curve are obtained for Fe/Au/Fe/MgO multilayers by magnetic Compton scattering and SQUID magnetometer measurements. The SSMH curve with each contribution of magnetic quantum number |m| = 0, 1, and 2 states is obtained by decomposition analyses of magnetic Compton profiles. Residual magnetization is observed for the SSMH curve with magnetic quantum number |m| = 0, 2 and the OSMH curve. Although the SQUID magnetometer measurements do not show perpendicular magnetic anisotropy (PMA) in the present Fe/Au/Fe/MgO multilayer film, the SSMH curve with magnetic quantum number |m| = 0, 2 and OSMH curve show switching behaviors of PMA.
Magnetic quantum coherence effect in Ni4 molecular transistors.
González, Gabriel; Leuenberger, Michael N
2014-07-01
We present a theoretical study of electron transport in Ni4 molecular transistors in the presence of Zeeman spin splitting and magnetic quantum coherence (MQC). The Zeeman interaction is extended along the leads which produces gaps in the energy spectrum which allow electron transport with spin polarized along a certain direction. We show that the coherent states in resonance with the spin up or down states in the leads induces an effective coupling between localized spin states and continuum spin states in the single molecule magnet and leads, respectively. We investigate the conductance at zero temperature as a function of the applied bias and magnetic field by means of the Landauer formula, and show that the MQC is responsible for the appearence of resonances. Accordingly, we name them MQC resonances. PMID:24918902
Magnetic quantum coherence effect in Ni4 molecular transistors.
González, Gabriel; Leuenberger, Michael N
2014-07-01
We present a theoretical study of electron transport in Ni4 molecular transistors in the presence of Zeeman spin splitting and magnetic quantum coherence (MQC). The Zeeman interaction is extended along the leads which produces gaps in the energy spectrum which allow electron transport with spin polarized along a certain direction. We show that the coherent states in resonance with the spin up or down states in the leads induces an effective coupling between localized spin states and continuum spin states in the single molecule magnet and leads, respectively. We investigate the conductance at zero temperature as a function of the applied bias and magnetic field by means of the Landauer formula, and show that the MQC is responsible for the appearence of resonances. Accordingly, we name them MQC resonances.
Quantum engineering of spin and anisotropy in magnetic molecular junctions.
Jacobson, Peter; Herden, Tobias; Muenks, Matthias; Laskin, Gennadii; Brovko, Oleg; Stepanyuk, Valeri; Ternes, Markus; Kern, Klaus
2015-01-01
Single molecule magnets and single spin centres can be individually addressed when coupled to contacts forming an electrical junction. To control and engineer the magnetism of quantum devices, it is necessary to quantify how the structural and chemical environment of the junction affects the spin centre. Metrics such as coordination number or symmetry provide a simple method to quantify the local environment, but neglect the many-body interactions of an impurity spin coupled to contacts. Here, we utilize a highly corrugated hexagonal boron nitride monolayer to mediate the coupling between a cobalt spin in CoHx (x=1,2) complexes and the metal contact. While hydrogen controls the total effective spin, the corrugation smoothly tunes the Kondo exchange interaction between the spin and the underlying metal. Using scanning tunnelling microscopy and spectroscopy together with numerical simulations, we quantitatively demonstrate how the Kondo exchange interaction mimics chemical tailoring and changes the magnetic anisotropy. PMID:26456084
Enhanced current injection from a quantum well to a quantum dash in magnetic field
NASA Astrophysics Data System (ADS)
Paravicini-Bagliani, Gian L.; Liverini, Valeria; Valmorra, Federico; Scalari, Giacomo; Gramm, Fabian; Faist, Jérôme
2014-08-01
Resonant tunneling injection is a key ingredient in achieving population inversion in a putative quantum dot cascade laser. In a quantum dot based structure, such resonant current requires a matching of the wavefunction shape in k-space between the injector and the quantum dot. We show experimentally that the injection into an excited state of a dash structure can be enhanced tenfold by an in-plane magnetic field that shifts the injector distribution in k-space. These experiments, performed on resonant tunneling diode structures, show unambiguously resonant tunneling into an ensemble of InAs dashes grown between two AlInAs barrier layers. They also show that interface roughness scattering can enhance the tunneling current.
Transverse quantum Stern-Gerlach magnets for electrons
NASA Astrophysics Data System (ADS)
McGregor, Scot; Bach, Roger; Batelaan, Herman
2011-06-01
In the Stern-Gerlach experiment, silver atoms were separated according to their spin state (Gerlach and Stern 1922 Z. Phys. 9 353-355). This experiment demonstrates the quantization of spin and relies on the classical description of motion. However, so far, no design has led to a functional Stern-Gerlach magnet for free electrons. Bohr and Pauli showed in the 1930 Solvay conference that Stern-Gerlach magnets for electrons cannot work, at least if the design is based on classical trajectories (Pauli W 1932 Proc. of the 6th Solvay Conf. 2 (1930) (Brussels: Gauthier-Villars) pp 183-86, 217-20, 275-80 Pauli W 1964 Collected Scientific Papers ed R Kronig and V F Weiskopf, vol 2 (New York: Wiley)). Here, we present ideas for the realization of a Stern-Gerlach magnet for electrons in which spin and motion are treated fully quantum mechanically. We show that a magnetic phase grating composed of a regular array of microscopic current loops can separate electron diffraction peaks according to their spin states. The experimental feasibility of a diffractive approach is compared to that of an interferometric approach. We show that an interferometric arrangement with magnetic phase control is the functional equivalent of an electron Stern-Gerlach magnet.
Quantum spin ice: a search for gapless quantum spin liquids in pyrochlore magnets.
Gingras, M J P; McClarty, P A
2014-05-01
The spin ice materials, including Ho2Ti2O7 and Dy2Ti2O7, are rare-earth pyrochlore magnets which, at low temperatures, enter a constrained paramagnetic state with an emergent gauge freedom. Spin ices provide one of very few experimentally realized examples of fractionalization because their elementary excitations can be regarded as magnetic monopoles and, over some temperature range, spin ice materials are best described as liquids of these emergent charges. In the presence of quantum fluctuations, one can obtain, in principle, a quantum spin liquid descended from the classical spin ice state characterized by emergent photon-like excitations. Whereas in classical spin ices the excitations are akin to electrostatic charges with a mutual Coulomb interaction, in the quantum spin liquid these charges interact through a dynamic and emergent electromagnetic field. In this review, we describe the latest developments in the study of such a quantum spin ice, focusing on the spin liquid phenomenology and the kinds of materials where such a phase might be found.
Externally controlled local magnetic field in a conducting mesoscopic ring coupled to a quantum wire
Maiti, Santanu K.
2015-01-14
In the present work, the possibility of regulating local magnetic field in a quantum ring is investigated theoretically. The ring is coupled to a quantum wire and subjected to an in-plane electric field. Under a finite bias voltage across the wire a net circulating current is established in the ring which produces a strong magnetic field at its centre. This magnetic field can be tuned externally in a wide range by regulating the in-plane electric field, and thus, our present system can be utilized to control magnetic field at a specific region. The feasibility of this quantum system in designing spin-based quantum devices is also analyzed.
Electronic Magnetization of a Quantum Point Contact Measured by Nuclear Magnetic Resonance.
Kawamura, Minoru; Ono, Keiji; Stano, Peter; Kono, Kimitoshi; Aono, Tomosuke
2015-07-17
We report an electronic magnetization measurement of a quantum point contact (QPC) based on nuclear magnetic resonance (NMR) spectroscopy. We find that NMR signals can be detected by measuring the QPC conductance under in-plane magnetic fields. This makes it possible to measure, from Knight shifts of the NMR spectra, the electronic magnetization of a QPC containing only a few electron spins. The magnetization changes smoothly with the QPC potential barrier height and peaks at the conductance plateau of 0.5×2e^{2}/h. The observed features are well captured by a model calculation assuming a smooth potential barrier, supporting a no bound state origin of the 0.7 structure.
Electronic Magnetization of a Quantum Point Contact Measured by Nuclear Magnetic Resonance
NASA Astrophysics Data System (ADS)
Kawamura, Minoru; Ono, Keiji; Stano, Peter; Kono, Kimitoshi; Aono, Tomosuke
2015-07-01
We report an electronic magnetization measurement of a quantum point contact (QPC) based on nuclear magnetic resonance (NMR) spectroscopy. We find that NMR signals can be detected by measuring the QPC conductance under in-plane magnetic fields. This makes it possible to measure, from Knight shifts of the NMR spectra, the electronic magnetization of a QPC containing only a few electron spins. The magnetization changes smoothly with the QPC potential barrier height and peaks at the conductance plateau of 0.5 ×2 e2/h . The observed features are well captured by a model calculation assuming a smooth potential barrier, supporting a no bound state origin of the 0.7 structure.
The quantum needle of the avian magnetic compass.
Hiscock, Hamish G; Worster, Susannah; Kattnig, Daniel R; Steers, Charlotte; Jin, Ye; Manolopoulos, David E; Mouritsen, Henrik; Hore, P J
2016-04-26
Migratory birds have a light-dependent magnetic compass, the mechanism of which is thought to involve radical pairs formed photochemically in cryptochrome proteins in the retina. Theoretical descriptions of this compass have thus far been unable to account for the high precision with which birds are able to detect the direction of the Earth's magnetic field. Here we use coherent spin dynamics simulations to explore the behavior of realistic models of cryptochrome-based radical pairs. We show that when the spin coherence persists for longer than a few microseconds, the output of the sensor contains a sharp feature, referred to as a spike. The spike arises from avoided crossings of the quantum mechanical spin energy-levels of radicals formed in cryptochromes. Such a feature could deliver a heading precision sufficient to explain the navigational behavior of migratory birds in the wild. Our results (i) afford new insights into radical pair magnetoreception, (ii) suggest ways in which the performance of the compass could have been optimized by evolution, (iii) may provide the beginnings of an explanation for the magnetic disorientation of migratory birds exposed to anthropogenic electromagnetic noise, and (iv) suggest that radical pair magnetoreception may be more of a quantum biology phenomenon than previously realized. PMID:27044102
Far-from-equilibrium spin transport in Heisenberg quantum magnets.
Hild, Sebastian; Fukuhara, Takeshi; Schauß, Peter; Zeiher, Johannes; Knap, Michael; Demler, Eugene; Bloch, Immanuel; Gross, Christian
2014-10-01
We study experimentally the far-from-equilibrium dynamics in ferromagnetic Heisenberg quantum magnets realized with ultracold atoms in an optical lattice. After controlled imprinting of a spin spiral pattern with an adjustable wave vector, we measure the decay of the initial spin correlations through single-site resolved detection. On the experimentally accessible time scale of several exchange times, we find a profound dependence of the decay rate on the wave vector. In one-dimensional systems, we observe diffusionlike spin transport with a dimensionless diffusion coefficient of 0.22(1). We show how this behavior emerges from the microscopic properties of the closed quantum system. In contrast to the one-dimensional case, our transport measurements for two-dimensional Heisenberg systems indicate anomalous superdiffusion. PMID:25325657
Mitra, Avik; Sivapriya, K; Kumar, Anil
2007-08-01
In a three player quantum 'Dilemma' game each player takes independent decisions to maximize his/her individual gain. The optimal strategy in the quantum version of this game has a higher payoff compared to its classical counterpart. However, this advantage is lost if the initial qubits provided to the players are from a noisy source. We have experimentally implemented the three player quantum version of the 'Dilemma' game as described by Johnson, [N.F. Johnson, Phys. Rev. A 63 (2001) 020302(R)] using nuclear magnetic resonance quantum information processor and have experimentally verified that the payoff of the quantum game for various levels of corruption matches the theoretical payoff.
Magnetic phase diagram of non-magnetic few-electron quantum dot molecules
NASA Astrophysics Data System (ADS)
Ribeiro-Santos, D., Jr.; Qu, Fanyao; Lopez-Richard, V.; Marques, G. E.
2012-02-01
A pathway to design non-magnetic artificial molecules which display controllable magnetic properties is addressed theoretically by studying the effects of in-plane electrical field, spin-orbit interaction (SOI) and geometrical parameters on the magnetic phase transitions in few-electron lateral double quantum dots (DQDs). We demonstrate the tunability of the magnetic phase diagram of two-electron DQDs as the system is changed from a molecule to an atom, in both weak and strong SOI regimes. We find an unusual jump in the magnetization and an asymmetric peak of the magnetic susceptibility. In addition, both the asymmetric susceptibility peak position and the magnetic phase diagram are strongly dependent on the interdot tunnel coupling, which can be tuned effectively by changing repulsive barrier voltage and/or interdot distance, the number of electrons and the SOI strength. With increasing interdot tunnel-coupling strength, for instance, the rate of paramagnetic-to-diamagnetic phase area increases. The SOI makes the paramagnetic phase more stable under magnetic field. Moreover, the effects of geometry deviation on the electronic structure and magnetic property of the DQD are also discussed.
Spectrum of a magnetized strong-leg quantum spin ladder.
Schmidiger, D; Bouillot, P; Guidi, T; Bewley, R; Kollath, C; Giamarchi, T; Zheludev, A
2013-09-01
Inelastic neutron scattering is used to measure the spin excitation spectrum of the Heisenberg S=1/2 ladder material (C7H10N)2CuBr4 in its entirety, both in the gapped spin liquid and the magnetic field-induced Tomonaga-Luttinger spin liquid regimes. A fundamental change of the spin dynamics is observed between these two regimes. Density matrix renormalization group calculations quantitatively reproduce and help understand the observed commensurate and incommensurate excitations. The results validate long-standing quantum field-theoretical predictions but also test the limits of that approach. PMID:25166704
Quantum tunneling of the magnetic moment in the S/F/S Josephson φ0 junction
NASA Astrophysics Data System (ADS)
Chudnovsky, Eugene M.
2016-04-01
We show that the S/F/S Josephson φ0 junction permits detection of macroscopic quantum tunneling and quantum oscillation of the magnetic moment by measuring the ac voltage across the junction. Exact expression for the tunnel splitting renormalized by the interaction with the superconducting order parameter is obtained. It is demonstrated that magnetic tunneling may become frozen at a sufficiently large φ0. The quality factor of quantum oscillations of the magnetic moment due to finite ohmic resistance of the junction is computed. It is shown that magnetic tunneling rate in the φ0 junction can be controlled by the bias current, with no need for the magnetic field.
Pressure-Induced Foaming of Metals
NASA Astrophysics Data System (ADS)
García-Moreno, Francisco; Mukherjee, Manas; Jiménez, Catalina; Banhart, John
2015-05-01
Pressure-induced foaming (PIF) of metals is a foaming technique in which blowing agent free compacted metal powders are foamed. The method consists of heating hot-compacted metallic precursors to above their melting temperature under gas overpressure and foaming them by pressure release. This study focuses on PIF of Al99.7 and AlSi7 alloys under both air or Ar and overpressures up to 9 bar. In situ x-ray radioscopy allows us to follow the foaming process and to perform quantitative analyses of expansion, foam morphology, and coalescence rate. Mass spectrometry helps to identify hydrogen as the foaming gas. Adsorbates on the former powder particles are found to be the primary gas source. Various advantages of this new method are identified and discussed.
Pressure-induced metallization of silane
Chen,X.; Struzhkin, V.; Song, Y.; Goncharov, A.; Ahart, M.; Liu, Z.; Mao, H.; Hemley, R.
2008-01-01
There is a great interest in electronic transitions in hydrogen-rich materials under extreme conditions. It has been recently suggested that the group IVa hydrides such as methane (CH4), silane (SiH4), and germane (GeH4) become metallic at far lower pressures than pure hydrogen at equivalent densities because the hydrogen is chemically compressed in group IVa hydride compounds. Here we report measurements of Raman and infrared spectra of silane under pressure. We find that SiH4 undergoes three phase transitions before becoming opaque at 27-30 GPa. The vibrational spectra indicate the material transforms to a polymeric (framework) structure in this higher pressure range. Room-temperature infrared reflectivity data reveal that the material exhibits Drude-like metallic behavior above 60 GPa, indicating the onset of pressure-induced metallization.
Radiation-pressure-induced nonlinearity in microdroplets.
Zhang, Peng; Jung, Sunghwan; Lee, Aram; Xu, Yong
2015-12-01
High quality (Q) factor whispering gallery modes (WGMs) can induce nonlinear effects in liquid droplets through mechanisms such as radiation pressure, Kerr nonlinearity, and thermal effects. However, such nonlinear effects, especially those due to radiation pressure, have yet to be thoroughly investigated and compared in the literature. In this study, we present an analytical approach that can exactly calculate the droplet deformation induced by the radiation pressure. The accuracy of the analytical approach is confirmed through numerical analyses based on the boundary element method. We show that the nonlinear optofluidic effect induced by the radiation pressure is stronger than the Kerr effect and the thermal effect under a large variety of realistic conditions. Using liquids with ultralow and experimentally attainable interfacial tension, we further confirm the prediction that it may only take a few photons to produce measurable WGM resonance shift through radiation-pressure-induced droplet deformation. PMID:26764829
Magnetic edge states in Aharonov-Bohm graphene quantum rings
Farghadan, R. Heidari Semiromi, E.; Saffarzadeh, A.
2013-12-07
The effect of electron-electron interaction on the electronic structure of Aharonov-Bohm (AB) graphene quantum rings (GQRs) is explored theoretically using the single-band tight-binding Hamiltonian and the mean-field Hubbard model. The electronic states and magnetic properties of hexagonal, triangular, and circular GQRs with different sizes and zigzag edge terminations are studied. The results show that, although the AB oscillations in the all types of nanoring are affected by the interaction, the spin splitting in the AB oscillations strongly depends on the geometry and the size of graphene nanorings. We found that the total spin of hexagonal and circular rings is zero and therefore, no spin splitting can be observed in the AB oscillations. However, the non-zero magnetization of the triangular rings breaks the degeneracy between spin-up and spin-down electrons, which produces spin-polarized AB oscillations.
Magnetic quantum well states in ultrathin film and wedge structures
Li, D.; Bader, S.D.
1996-04-01
Magnetic quantum-well (QW) states are probed with angle- and spin-resolved photoemission to address critical issues pertaining to the origin of the giant magnetoresistance (GMR) optimization and oscillatory coupling of magnetic multilayers. Two epitaxial systems are highlighted: Cu/Co(wedge)/Cu(100) and Cr/Fe(100)-whisker. The confinement of Cu sp-QW states by a Co barrier requires a characteristic Co thickness of 2.2 {+-} 0.6 {angstrom}, which is consistent with the interfacial Co thickness reported to optimize the GMR of permalloy-Cu structures. The controversial k-space origin of the 18-{angstrom} long period oscillation in Fe/Cr multilayers is identified by the vector that spans the d-derived lens feature of the Cr Fermi surface, based on the emergence of QW states with 17 {+-} 2 {angstrom} periodicity in this region.
Nuclear magnetization in gallium arsenide quantum dots at zero magnetic field.
Sallen, G; Kunz, S; Amand, T; Bouet, L; Kuroda, T; Mano, T; Paget, D; Krebs, O; Marie, X; Sakoda, K; Urbaszek, B
2014-01-01
Optical and electrical control of the nuclear spin system allows enhancing the sensitivity of NMR applications and spin-based information storage and processing. Dynamic nuclear polarization in semiconductors is commonly achieved in the presence of a stabilizing external magnetic field. Here we report efficient optical pumping of nuclear spins at zero magnetic field in strain-free GaAs quantum dots. The strong interaction of a single, optically injected electron spin with the nuclear spins acts as a stabilizing, effective magnetic field (Knight field) on the nuclei. We optically tune the Knight field amplitude and direction. In combination with a small transverse magnetic field, we are able to control the longitudinal and transverse components of the nuclear spin polarization in the absence of lattice strain--that is, in dots with strongly reduced static nuclear quadrupole effects, as reproduced by our model calculations.
Controlling magnetic order and quantum disorder in molecule-based magnets.
Lancaster, T.; Goddard, P. A.; Blundell, S. J.; Foronda, F. R.; Ghannadzadeh, S.; Moller, J. S.; Baker, P. J.; Pratt, F. L.; Baines, C.; Huang, L.; Schlueter, J. A.
2014-05-19
We investigate the structural and magnetic properties of two molecule-based magnets synthesized from the same starting components. Their different structural motifs promote contrasting exchange pathways and consequently lead to markedly different magnetic ground states. Through examination of their structural and magnetic properties we show that [Cu(pyz)(H 2 O)(gly) 2 ](ClO 4 ) 2 may be considered a quasi-one-dimensional quantum Heisenberg antiferromagnet whereas the related compound [Cu(pyz)(gly)](ClO 4 ) , which is formed from dimers of antiferromagnetically interacting Cu 2+ spins, remains disordered down to at least 0.03 K in zero field but shows a field-temperature phase diagram reminiscent of that seen in materials showing a Bose-Einstein condensation of magnons.
The quantum field theory of electric and magnetic charge
NASA Astrophysics Data System (ADS)
Blagojević, M.; Senjanović, P.
1988-01-01
The dynamics of monopoles as quantum objects is described by the quantum field theory of monopoles and charges. Owing to the presence of a preferred direction n, this is the first example of a theory which is not manifestly Lorentz invariant, though intrinsically it possesses this invariance. Another unusual property of this Abelian theory is that it has two coupling constants connected via the quatization condition. The investigation of the basic properties of the theory is facilitated by the existence of various formulations. Thus, Lorentz invariance, which is not easily seen in Schwinger's Hamiltonian framework, is transparent after the introduction of the particle-path representation of Zwanziger's local Langrarian formulation. Ultraviolet properties of the theory receive a superior, n-independent treatment in this representation, with the result that favors opposite renormalization of electric and magnetic charge. The physical content of infrared regularization is clearly described in the one-potential formulation. Several other topics are treated: Dirac's quantum mechanics of the monopole, connection with non-Abelian monopoles, a supersymmetric generalization of the theory, and its possible role in preon dynamics.
Microtesla magnetic resonance imaging with a superconducting quantum interference device
McDermott, Robert; Lee, SeungKyun; ten Haken, Bennie; Trabesinger, Andreas H.; Pines, Alexander; Clarke, John
2004-03-15
We have constructed a magnetic resonance imaging (MRI) scanner based on a dc Superconducting QUantum Interference Device (SQUID) configured as a second-derivative gradiometer. The magnetic field sensitivity of the detector is independent of frequency; it is therefore possible to obtain high-resolution images by prepolarizing the nuclear spins in a field of 300 mT and detecting the signal at 132 fYT, corresponding to a proton Larmor frequency of 5.6 kHz. The reduction in the measurement field by a factor of 10,000 compared with conventional scanners eliminates inhomogeneous broadening of the nuclear magnetic resonance lines, even in fields with relatively poor homogeneity. The narrow linewidths result in enhanced signal-to-noise ratio and spatial resolution for a fixed strength of the magnetic field gradients used to encode the image. We present two-dimensional images of phantoms and pepper slices, obtained in typical magnetic field gradients of 100 fYT/m, with a spatial resolution of about 1mm. We further demonstrate a slice-selected image of an intact pepper. By varying the time delay between removal of the polarizing field and initiation of the spin echo sequence we acquire T1-weighted contrast images of water phantoms, some of which are doped with a paramagnetic salt; here, T1 is the nuclear spin-lattice relaxation time. The techniques presented here could readily be adapted to existing multichannel SQUID systems used for magnetic source imaging of brain signals. Further potential applications include low-cost systems for tumor screening and imaging peripheral regions of the body.
Quantum control of proximal spins using nanoscale magnetic resonance imaging
NASA Astrophysics Data System (ADS)
Grinolds, M. S.; Maletinsky, P.; Hong, S.; Lukin, M. D.; Walsworth, R. L.; Yacoby, A.
2011-09-01
Quantum control of individual spins in condensed-matter systems is an emerging field with wide-ranging applications in spintronics, quantum computation and sensitive magnetometry. Recent experiments have demonstrated the ability to address and manipulate single electron spins through either optical or electrical techniques. However, it is a challenge to extend individual-spin control to nanometre-scale multi-electron systems, as individual spins are often irresolvable with existing methods. Here we demonstrate that coherent individual-spin control can be achieved with few- nanometre resolution for proximal electron spins by carrying out single-spin magnetic resonance imaging (MRI), which is realized using a scanning-magnetic-field gradient that is both strong enough to achieve nanometre spatial resolution and sufficiently stable for coherent spin manipulations. We apply this scanning-field-gradient MRI technique to electronic spins in nitrogen-vacancy (NV) centres in diamond and achieve nanometre resolution in imaging, characterization and manipulation of individual spins. For NV centres, our results in individual-spin control demonstrate an improvement of nearly two orders of magnitude in spatial resolution when compared with conventional optical diffraction-limited techniques. This scanning-field-gradient microscope enables a wide range of applications including materials characterization, spin entanglement and nanoscale magnetometry.
A magnetically induced quantum critical point in holography
NASA Astrophysics Data System (ADS)
Gnecchi, A.; Gursoy, U.; Papadoulaki, O.; Toldo, C.
2016-09-01
We investigate quantum critical points in a 2+1 dimensional gauge theory at finite chemical potential χ and magnetic field B. The gravity dual is based on 4D N = 2 Fayet-Iliopoulos gauged supergravity and the solutions we consider — that are constructed analytically — are extremal, dyonic, asymptotically AdS 4 black-branes with a nontrivial radial profile for the scalar field. We discover a line of second order fixed points at B = B c (χ) between the dyonic black brane and an extremal "thermal gas" solution with a singularity of good-type, according to the acceptability criteria of Gubser [1]. The dual field theory is a strongly coupled nonconformal field theory at finite charge and magnetic field, related to the ABJM theory [2] deformed by a triple trace operator Φ3. This line of fixed points might be useful in studying the various strongly interacting quantum critical phenomena such as the ones proposed to underlie the cuprate superconductors. We also find curious similarities between the behaviour of the VeV <Φ> under B and that of the quark condensate in 2+1 dimensional NJL models.
Linear and nonlinear quantum ion-acoustic waves in dense magnetized electron-positron-ion plasmas
Khan, S. A.; Masood, W.
2008-06-15
The linear and nonlinear quantum ion-acoustic waves propagating obliquely in two dimensions in superdense, magnetized electron-positron-ion quantum plasma are investigated on the basis of quantum hydrodynamic model. It is found in linear analysis that the quantum corrections of diffraction are important in the very short wavelength regime that may be found in dense astrophysical plasmas. To investigate the solitary waves, the Zakharov-Kuznetsov equation is derived and the solution is presented in the small amplitude limit. By numerical analysis, it is found that the soliton structure of the ion acoustic wave depends upon quantum pressure, concentration of positrons, strength of magnetic field, and the propagation angle.
Linear and nonlinear quantum ion-acoustic waves in dense magnetized electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Khan, S. A.; Masood, W.
2008-06-01
The linear and nonlinear quantum ion-acoustic waves propagating obliquely in two dimensions in superdense, magnetized electron-positron-ion quantum plasma are investigated on the basis of quantum hydrodynamic model. It is found in linear analysis that the quantum corrections of diffraction are important in the very short wavelength regime that may be found in dense astrophysical plasmas. To investigate the solitary waves, the Zakharov-Kuznetsov equation is derived and the solution is presented in the small amplitude limit. By numerical analysis, it is found that the soliton structure of the ion acoustic wave depends upon quantum pressure, concentration of positrons, strength of magnetic field, and the propagation angle.
NMR probing of quantum electron solids in high magnetic fields
NASA Astrophysics Data System (ADS)
Rhone, Trevor David
2015-03-01
In the presence of a high magnetic field, a two dimensional electron system (2DES) is expected to manifest Wigner crystal phases. Over thirty years ago, the search for the Wigner solid led to the discovery of the fractional quantum Hall effect (FQHE). Since then, with the advent of GaAs quantum wells with increasingly high mobility, 2DESs in the quantum Hall regime have proved to be a hunting ground for exceedingly rich many-body physics. Incompressible liquid FQHE states were found to occur in the first Landau level at several fractional filling factors v with odd-denominator. The sequence of FQHE states is truncated by the formation of a Wigner crystal of electrons at very low filling factors, the transition being affected by disorder. In the second Landau level, composite fermions, the quasiparticles of the FQHE, can pair to yield a remarkable even-denominator FQHE state, whose properties are at the forefront of investigation. More recently, electron solid phases have been shown to emerge around integer quantum Hall states. In this talk, I will discuss a new tool, resistively detected NMR, which serves as a direct local probe of in-plane charge density modulations in the 2DES. In our recent work [1] we probe the local charge density landscape of Wigner solids in the vicinity of v = 2 and v<1/3 revealing quantum correlations. This unprecedented access to the microscopic behavior of these exotic solid phases opens up new venues in FQH studies. Furthermore, our NMR technique can probe in-plane charge density fluctuations due to disorder, allowing increased access to understanding roles of disorder in quantum Hall systems. In addition, our latest NMR measurements reveal evidence for charge inhomogeneity in the third Landau level which leads to the possibility of studying bubble and stripe phases in this regime. Future directions may find our NMR technique applied to other exotic phases such as quasiparticle solid phases, which have been proposed to emerge near the v
Bethe-Salpeter equation for exciton states in quantum well in a nonhomogeneous magnetic field
NASA Astrophysics Data System (ADS)
Koinov, Z.; Nash, P.; Witzel, J.
2003-03-01
The trapping of excitons in a single quantum well due to the presence of an external strong constant magnetic field and a small nonhomogeneous cylindrical symmetric magnetic field, created by a magnetized disk on top of the quantum well, is studied by applying the Bethe-Salpeter formalism. The numerical calculations are performed for GaAs/AlGaAs quantum wells. We find that the nonhomogeneous magnetic field leads to the formation of bound exciton states with nonzero values for the center-of-mass exciton wave function only in a sufficiently small area.
Quantum Monte Carlo Calculations Applied to Magnetic Molecules
Engelhardt, Larry
2006-01-01
We have calculated the equilibrium thermodynamic properties of Heisenberg spin systems using a quantum Monte Carlo (QMC) method. We have used some of these systems as models to describe recently synthesized magnetic molecules, and-upon comparing the results of these calculations with experimental data-have obtained accurate estimates for the basic parameters of these models. We have also performed calculations for other systems that are of more general interest, being relevant both for existing experimental data and for future experiments. Utilizing the concept of importance sampling, these calculations can be carried out in an arbitrarily large quantum Hilbert space, while still avoiding any approximations that would introduce systematic errors. The only errors are statistical in nature, and as such, their magnitudes are accurately estimated during the course of a simulation. Frustrated spin systems present a major challenge to the QMC method, nevertheless, in many instances progress can be made. In this chapter, the field of magnetic molecules is introduced, paying particular attention to the characteristics that distinguish magnetic molecules from other systems that are studied in condensed matter physics. We briefly outline the typical path by which we learn about magnetic molecules, which requires a close relationship between experiments and theoretical calculations. The typical experiments are introduced here, while the theoretical methods are discussed in the next chapter. Each of these theoretical methods has a considerable limitation, also described in Chapter 2, which together serve to motivate the present work. As is shown throughout the later chapters, the present QMC method is often able to provide useful information where other methods fail. In Chapter 3, the use of Monte Carlo methods in statistical physics is reviewed, building up the fundamental ideas that are necessary in order to understand the method that has been used in this work. With these
Amaral, Jose Jussi; Wan, Jacky; Rodarte, Andrea L.; Ferri, Christopher; Quint, Makiko T.; Pandolfi, Ronald J.; Scheibner, Michael; Hirst, Linda S.; Ghosh, Sayantani
2014-10-22
The design and development of multifunctional composite materials from artificial nano-constituents is one of the most compelling current research areas. This drive to improve over nature and produce ‘meta-materials’ has met with some success, but results have proven limited with regards to both the demonstration of synergistic functionalities and in the ability to manipulate the material properties post-fabrication and in situ. Here, magnetic nanoparticles (MNPs) and semiconducting quantum dots (QDs) are co-assembled in a nematic liquid crystalline (LC) matrix, forming composite structures in which the emission intensity of the quantum dots is systematically and reversibly controlled with a small applied magnetic field (<100 mT). This magnetic field-driven brightening, ranging between a two- to three-fold peak intensity increase, is a truly cooperative effect: the LC phase transition creates the co-assemblies, the clustering of the MNPs produces LC re-orientation at atypical low external field, and this re-arrangement produces compaction of the clusters, resulting in the detection of increased QD emission. These results demonstrate a synergistic, reversible, and an all-optical process to detect magnetic fields and additionally, as the clusters are self-assembled in a fluid medium, they offer the possibility for these sensors to be used in broad ranging fluid-based applications.
Amaral, Jose Jussi; Wan, Jacky; Rodarte, Andrea L.; Ferri, Christopher; Quint, Makiko T.; Pandolfi, Ronald J.; Scheibner, Michael; Hirst, Linda S.; Ghosh, Sayantani
2014-10-22
The design and development of multifunctional composite materials from artificial nano-constituents is one of the most compelling current research areas. This drive to improve over nature and produce ‘meta-materials’ has met with some success, but results have proven limited with regards to both the demonstration of synergistic functionalities and in the ability to manipulate the material properties post-fabrication and in situ. Here, magnetic nanoparticles (MNPs) and semiconducting quantum dots (QDs) are co-assembled in a nematic liquid crystalline (LC) matrix, forming composite structures in which the emission intensity of the quantum dots is systematically and reversibly controlled with a small appliedmore » magnetic field (<100 mT). This magnetic field-driven brightening, ranging between a two- to three-fold peak intensity increase, is a truly cooperative effect: the LC phase transition creates the co-assemblies, the clustering of the MNPs produces LC re-orientation at atypical low external field, and this re-arrangement produces compaction of the clusters, resulting in the detection of increased QD emission. These results demonstrate a synergistic, reversible, and an all-optical process to detect magnetic fields and additionally, as the clusters are self-assembled in a fluid medium, they offer the possibility for these sensors to be used in broad ranging fluid-based applications.« less
Magnetic reversal dynamics of a quantum system on a picosecond timescale
Kuznetsov, Alexey V; Soloviev, Igor I; Bakurskiy, Sergey V; Tikhonova, Olga V
2015-01-01
Summary We present our approach for a consistent, fully quantum mechanical description of the magnetization reversal process in natural and artificial atomic systems by means of short magnetic pulses. In terms of the simplest model of a two-level system with a magnetic moment, we analyze the possibility of a fast magnetization reversal on the picosecond timescale induced by oscillating or short unipolar magnetic pulses. We demonstrate the possibility of selective magnetization reversal of a superconducting flux qubit using a single flux quantum-based pulse and suggest a promising, rapid Λ-scheme for resonant implementation of this process. In addition, the magnetization reversal treatment is fulfilled within the framework of the macroscopic theory of the magnetic moment, which allows for the comparison and explanation of the quantum and classical behavior. PMID:26665066
Magnetic reversal dynamics of a quantum system on a picosecond timescale.
Klenov, Nikolay V; Kuznetsov, Alexey V; Soloviev, Igor I; Bakurskiy, Sergey V; Tikhonova, Olga V
2015-01-01
We present our approach for a consistent, fully quantum mechanical description of the magnetization reversal process in natural and artificial atomic systems by means of short magnetic pulses. In terms of the simplest model of a two-level system with a magnetic moment, we analyze the possibility of a fast magnetization reversal on the picosecond timescale induced by oscillating or short unipolar magnetic pulses. We demonstrate the possibility of selective magnetization reversal of a superconducting flux qubit using a single flux quantum-based pulse and suggest a promising, rapid Λ-scheme for resonant implementation of this process. In addition, the magnetization reversal treatment is fulfilled within the framework of the macroscopic theory of the magnetic moment, which allows for the comparison and explanation of the quantum and classical behavior. PMID:26665066
AA-stacked bilayer graphene quantum dots in magnetic field
NASA Astrophysics Data System (ADS)
Belouad, Abdelhadi; Zahidi, Youness; Jellal, Ahmed
2016-05-01
By applying the infinite-mass boundary condition, we analytically calculate the confined states and the corresponding wave functions of AA-stacked bilayer graphene (BLG) quantum dots (QDs) in the presence of an uniform magnetic field B. It is found that the energy spectrum shows two set of levels, which are the double copies of the energy spectrum for single layer graphene, shifted up–down by +γ and -γ , respectively. However, the obtained spectrum exhibits different symmetries between the electron and hole states as well as the intervalley symmetries. It is noticed that, the applied magnetic field breaks all symmetries, except one related to the intervalley electron–hole symmetry, i.e. {E}{{e}}(τ ,m)=-{E}{{h}}(τ ,m). Two different regimes of confinement are found: the first one is due to the infinite-mass barrier at weak B and the second is dominated by the magnetic field as long as B is large. We numerically investigated the basics features of the energy spectrum to show the main similarities and differences with respect to monolayer graphene, AB-stacked BLG and semiconductor QDs. Dedicated to Professor Dr Hachim A Yamani on the occasion of his 70th birthday.
Quantum Monte Carlo study of magnetic impurity in bilayer grephene
NASA Astrophysics Data System (ADS)
Sun, J. H.; Hu, F. M.; Tang, H. K.; Lin, Hai-Qing
2012-02-01
It is expected to observe many different properties in bilayer graphene when compared with single layer graphene due to the differences in crystal structure. Additionally, bilayer system offers a freedom of inducing a gap in the energy band by applying a shift in the electrochemical potential to two graphene layers. In this work, we study the magnetic properties of an Anderson magnetic adatom in Bernal stacking bilayer graphene and compare the results with those of single layer counterpart. Several different cases such as different adatom position and different potential bias of two layers are studied using the quantum Monte Carlo method. In all the cases, we find that the impurity local magnetic moment can be switched between relatively large and small values by tuning the chemical potential. We apply MaxEnT method to compute impurity spectral density and find its behavior to differ from that of an impurity in a single layer graphene. We also calculate various correlation functions and make comparisons.
Quantum Hall states stabilized in semi-magnetic bilayers of topological insulators
Yoshimi, R.; Yasuda, K.; Tsukazaki, A.; Takahashi, K. S.; Nagaosa, N.; Kawasaki, M.; Tokura, Y.
2015-01-01
By breaking the time-reversal symmetry in three-dimensional topological insulators with the introduction of spontaneous magnetization or application of magnetic field, the surface states become gapped, leading to quantum anomalous Hall effect or quantum Hall effect, when the chemical potential locates inside the gap. Further breaking of inversion symmetry is possible by employing magnetic topological insulator heterostructures that host non-degenerate top and bottom surface states. Here we demonstrate the tailored-material approach for the realization of robust quantum Hall states in the bilayer system, in which the cooperative or cancelling combination of the anomalous and ordinary Hall responses from the respective magnetic and non-magnetic layers is exemplified. The appearance of quantum Hall states at filling factor 0 and +1 can be understood by the relationship of energy band diagrams for the two independent surface states. The designable heterostructures of magnetic topological insulator may explore a new arena for intriguing topological transport and functionality. PMID:26497065
Quantum critical behavior in heavy electron materials
Yang, Yi-feng; Pines, David
2014-01-01
Quantum critical behavior in heavy electron materials is typically brought about by changes in pressure or magnetic field. In this paper, we develop a simple unified model for the combined influence of pressure and magnetic field on the effectiveness of the hybridization that plays a central role in the two-fluid description of heavy electron emergence. We show that it leads to quantum critical and delocalization lines that accord well with those measured for CeCoIn5, yields a quantitative explanation of the field and pressure-induced changes in antiferromagnetic ordering and quantum critical behavior measured for YbRh2Si2, and provides a valuable framework for describing the role of magnetic fields in bringing about quantum critical behavior in other heavy electron materials. PMID:24912172
Trichoscopy of Noncicatricial Pressure-induced Alopecia Resembling Alopecia Areata.
Papaiordanou, Francine; da Silveira, Bruno Rebelo Lages; Piñeiro-Maceira, Juan; Pirmez, Rodrigo
2016-01-01
Pressure-induced alopecia is an unusual cause of hair loss, and reports of its trichoscopic features are scarce. In this paper, we describe a case of pressure-induced alopecia in which trichoscopic and histopathological findings overlap with those described for alopecia areata. PMID:27601865
Trichoscopy of Noncicatricial Pressure-induced Alopecia Resembling Alopecia Areata
Papaiordanou, Francine; da Silveira, Bruno Rebelo Lages; Piñeiro-Maceira, Juan; Pirmez, Rodrigo
2016-01-01
Pressure-induced alopecia is an unusual cause of hair loss, and reports of its trichoscopic features are scarce. In this paper, we describe a case of pressure-induced alopecia in which trichoscopic and histopathological findings overlap with those described for alopecia areata. PMID:27601865
Chern-Simons theory for frustrated quantum magnets
NASA Astrophysics Data System (ADS)
Kumar, Krishna; Fradkin, Eduardo
2013-03-01
We study the problem of frustrated quantum magnets by mapping models with Heisenberg spins, which are hard-core bosons, onto a problem of fermions coupled to a Chern-Simons gauge field. Similar methods have been used successfully in the case of unfrustrated systems like the square lattice. However, in the case of frustrated systems there always exists some arbitrariness in defining the problem. At the mean-field level these issues can be over looked but the effects of fluctuations, which are generally strong in these systems, are expected to alter the mean-field physics. We discuss the difficulties involved in setting up this problem on a triangular or kagome lattice and some approaches to tackle these issues. We study the effects of fluctuations in these systems and the possibility of spin-liquid type phases.
Nuclear-magnetic-resonance quantum calculations of the Jones polynomial
Marx, Raimund; Spoerl, Andreas; Pomplun, Nikolas; Schulte-Herbrueggen, Thomas; Glaser, Steffen J.; Fahmy, Amr; Kauffman, Louis; Lomonaco, Samuel; Myers, John M.
2010-03-15
The repertoire of problems theoretically solvable by a quantum computer recently expanded to include the approximate evaluation of knot invariants, specifically the Jones polynomial. The experimental implementation of this evaluation, however, involves many known experimental challenges. Here we present experimental results for a small-scale approximate evaluation of the Jones polynomial by nuclear magnetic resonance (NMR); in addition, we show how to escape from the limitations of NMR approaches that employ pseudopure states. Specifically, we use two spin-1/2 nuclei of natural abundance chloroform and apply a sequence of unitary transforms representing the trefoil knot, the figure-eight knot, and the Borromean rings. After measuring the nuclear spin state of the molecule in each case, we are able to estimate the value of the Jones polynomial for each of the knots.
Two-dimensional quantum walk under artificial magnetic field
NASA Astrophysics Data System (ADS)
Yalcinkaya, Iskender; Gedik, Zafer
We introduce the Peierls substitution to a two-dimensional discrete-time quantum walk on a square lattice to examine the spreading dynamics and the coin-position entanglement in the presence of an artificial gauge field. We use the ratio of the magnetic flux through the unit cell to the flux quantum as a control parameter. For a given flux ratio, we obtain faster spreading for a small number of steps and the walker tends to be highly localized around the origin. Moreover, the spreading of the walk can be suppressed and decreased within a limited time interval for specific rational values of flux ratio. When the flux ratio is an irrational number, even for a large number of steps, the spreading exhibit diffusive behavior rather than the well-known ballistic one as in the classical random walk and there is a significant probability of finding the walker at the origin. We also analyze the coin-position entanglement and show that the asymptotic behavior vanishes when the flux ratio is different from zero and the coin-position entanglement become nearly maximal in a periodic manner in a long time range.
Proximate Kitaev quantum spin liquid behaviour in a honeycomb magnet.
Banerjee, A; Bridges, C A; Yan, J-Q; Aczel, A A; Li, L; Stone, M B; Granroth, G E; Lumsden, M D; Yiu, Y; Knolle, J; Bhattacharjee, S; Kovrizhin, D L; Moessner, R; Tennant, D A; Mandrus, D G; Nagler, S E
2016-07-01
Quantum spin liquids (QSLs) are topological states of matter exhibiting remarkable properties such as the capacity to protect quantum information from decoherence. Whereas their featureless ground states have precluded their straightforward experimental identification, excited states are more revealing and particularly interesting owing to the emergence of fundamentally new excitations such as Majorana fermions. Ideal probes of these excitations are inelastic neutron scattering experiments. These we report here for a ruthenium-based material, α-RuCl3, continuing a major search (so far concentrated on iridium materials) for realizations of the celebrated Kitaev honeycomb topological QSL. Our measurements confirm the requisite strong spin-orbit coupling and low-temperature magnetic order matching predictions proximate to the QSL. We find stacking faults, inherent to the highly two-dimensional nature of the material, resolve an outstanding puzzle. Crucially, dynamical response measurements above interlayer energy scales are naturally accounted for in terms of deconfinement physics expected for QSLs. Comparing these with recent dynamical calculations involving gauge flux excitations and Majorana fermions of the pure Kitaev model, we propose the excitation spectrum of α-RuCl3 as a prime candidate for fractionalized Kitaev physics. PMID:27043779
Proximate Kitaev quantum spin liquid behaviour in a honeycomb magnet
Banerjee, A.; Bridges, C. A.; Yan, J. -Q.; Aczel, A. A.; Li, L.; Stone, M. B.; Granroth, G. E.; Lumsden, M. D.; Yiu, Y.; Knolle, J.; et al
2016-04-04
Quantum spin liquids (QSLs) are topological states of matter exhibiting remarkable properties such as the capacity to protect quantum information from decoherence. While their featureless ground states have precluded their straightforward experimental identification, excited states are more revealing and particularly interesting due to the emergence of fundamentally new excitations such as Majorana Fermions. Ideal probes of these excitations are inelastic neutron scattering experiments. We report these here for a ruthenium-based material α-RuCl3, continuing a major search (so far concentrated on iridium materials inimical to neutron probes) for realizations of the celebrated Kitaev honeycomb topological QSL. Our measurements confirm the requisitemore » strong spin-orbit coupling and low-temperature magnetic order matching predictions proximate to the QSL. We find stacking faults, inherent to the highly 2D nature of the material, resolve an outstanding puzzle. Crucially, dynamical response measurements above interlayer energy scales are naturally accounted for in terms of deconfinement physics expected for QSLs. Comparing these with recent dynamical calculations involving gauge flux excitations and Majorana fermions of the pure Kitaev model, we propose the excitation spectrum of α-RuCl3 as prime candidate for realization of fractionalized Kitaev physics.« less
Quantum magnetic phase transition in square-octagon lattice
NASA Astrophysics Data System (ADS)
Bao, An; Tao, Hong-Shuai; Liu, Hai-Di; Zhang, Xiaozhong; Liu, Wu-Ming
2014-11-01
Quantum magnetic phase transition in square-octagon lattice was investigated by cellular dynamical mean field theory combining with continuous time quantum Monte Carlo algorithm. Based on the systematic calculation on the density of states, the double occupancy and the Fermi surface evolution of square-octagon lattice, we presented the phase diagrams of this splendid many particle system. The competition between the temperature and the on-site repulsive interaction in the isotropic square-octagon lattice has shown that both antiferromagnetic and paramagnetic order can be found not only in the metal phase, but also in the insulating phase. Antiferromagnetic metal phase disappeared in the phase diagram that consists of the anisotropic parameter λ and the on-site repulsive interaction U while the other phases still can be detected at T = 0.17. The results found in this work may contribute to understand well the properties of some consuming systems that have square-octagon structure, quasi square-octagon structure, such as ZnO.
Pressure-induced exotic states in rare earth hexaborides.
Sun, Liling; Wu, Qi
2016-08-01
Finding the exotic phenomena in strongly correlated electron systems (SCESs) and understanding the corresponding microphysics have long been the research frontiers of condensed matter physics. The remarkable examples for the intriguing phenomena discovered in past years include unconventional superconductivity, heavy Fermion behaviors, giant magneto-resistance and so on. A fascinating type of rare earth hexaboride RB6 (R = Sm, Yb, Eu and Ce) belongs to a strongly correlated electron system (SCES), but shows unusual ambient-pressure and high-pressure behaviors beyond the phenomena mentioned above. Particularly, the recent discovery of the coexistence of an unusual metallic surface state and an insulating bulk state in SmB6, known to be a Kondo insulator decades ago, by theoretical calculations and many experimental measurements creates new interest for the investigation of the RB6. This significant progress encourages people to revisit the RB6 with an attempt to establish a new physics that links the SCES and the unusual metallic surface state which is a common feature of a topological insulator (TI). It is well known that pressure has the capability of tuning the electronic structure and modifying the ground state of solids, or even inducing a quantum phase transition which is one of the kernel issues in studies of SCESs. In this brief review, we will describe the progress in high pressure studies on the RB6 based on our knowledge and research interests, mainly focusing on the pressure-induced phenomena in YbB6 and SmB6, especially on the quantum phase transitions and their connections with the valence state of the rare earth ions. Moreover, some related high-pressure results obtained from CeB6 and EuB6 are also included. Finally, a summary is given in the conclusions and perspectives section. PMID:27376406
Pressure-induced exotic states in rare earth hexaborides
NASA Astrophysics Data System (ADS)
Sun, Liling; Wu, Qi
2016-08-01
Finding the exotic phenomena in strongly correlated electron systems (SCESs) and understanding the corresponding microphysics have long been the research frontiers of condensed matter physics. The remarkable examples for the intriguing phenomena discovered in past years include unconventional superconductivity, heavy Fermion behaviors, giant magneto-resistance and so on. A fascinating type of rare earth hexaboride RB6 (R = Sm, Yb, Eu and Ce) belongs to a strongly correlated electron system (SCES), but shows unusual ambient-pressure and high-pressure behaviors beyond the phenomena mentioned above. Particularly, the recent discovery of the coexistence of an unusual metallic surface state and an insulating bulk state in SmB6, known to be a Kondo insulator decades ago, by theoretical calculations and many experimental measurements creates new interest for the investigation of the RB6. This significant progress encourages people to revisit the RB6 with an attempt to establish a new physics that links the SCES and the unusual metallic surface state which is a common feature of a topological insulator (TI). It is well known that pressure has the capability of tuning the electronic structure and modifying the ground state of solids, or even inducing a quantum phase transition which is one of the kernel issues in studies of SCESs. In this brief review, we will describe the progress in high pressure studies on the RB6 based on our knowledge and research interests, mainly focusing on the pressure-induced phenomena in YbB6 and SmB6, especially on the quantum phase transitions and their connections with the valence state of the rare earth ions. Moreover, some related high-pressure results obtained from CeB6 and EuB6 are also included. Finally, a summary is given in the conclusions and perspectives section.
Pressure-induced decomposition of indium hydroxide.
Gurlo, Aleksander; Dzivenko, Dmytro; Andrade, Miria; Riedel, Ralf; Lauterbach, Stefan; Kleebe, Hans-Joachim
2010-09-15
A static pressure-induced decomposition of indium hydroxide into metallic indium that takes place at ambient temperature is reported. The lattice parameter of c-In(OH)(3) decreased upon compression from 7.977(2) to approximately 7.45 A at 34 GPa, corresponding to a decrease in specific volume of approximately 18%. Fitting the second-order Birch-Murnaghan equation of state to the obtained compression data gave a bulk modulus of 99 +/- 3 GPa for c-In(OH)(3). The c-In(OH)(3) crystals with a size of approximately 100 nm are comminuted upon compression, as indicated by the grain-size reduction reflected in broadening of the diffraction reflections and the appearance of smaller (approximately 5 nm) incoherently oriented domains in TEM. The rapid decompression of compressed c-In(OH)(3) leads to partial decomposition of indium hydroxide into metallic indium, mainly as a result of localized stress gradients caused by relaxation of the highly disordered indium sublattice in indium hydroxide. This partial decomposition of indium hydroxide into metallic indium is irreversible, as confirmed by angle-dispersive X-ray diffraction, transmission electron microscopy imaging, Raman scattering, and FTIR spectroscopy. Recovered c-In(OH)(3) samples become completely black and nontransparent and show typical features of metals, i.e., a falling absorption in the 100-250 cm(-1) region accompanied by a featureless spectrum in the 250-2500 cm(-1) region in the Raman spectrum and Drude-like absorption of free electrons in the region of 4000-8000 cm(-1) in the FTIR spectrum. These features were not observed in the initial c-In(OH)(3), which is a typical white wide-band-gap semiconductor.
NASA Astrophysics Data System (ADS)
Yu, Rong; Miclea, Corneliu F.; Weickert, Franziska; Movshovich, Roman; Paduan-Filho, Armando; Zapf, Vivien S.; Roscilde, Tommaso
2012-10-01
In this paper we investigate the quantum phase transition from magnetic Bose Glass to magnetic Bose-Einstein condensation induced by a magnetic field in NiCl2·4SC(NH2)2 (dichloro-tetrakis-thiourea-nickel, or DTN), doped with Br (Br-DTN) or site diluted. Quantum Monte Carlo simulations for the quantum phase transition of the model Hamiltonian for Br-DTN, as well as for site-diluted DTN, are consistent with conventional scaling at the quantum critical point and with a critical exponent z verifying the prediction z=d; moreover the correlation length exponent is found to be ν=0.75(10), and the order parameter exponent to be β=0.95(10). We investigate the low-temperature thermodynamics at the quantum critical field of Br-DTN both numerically and experimentally, and extract the power-law behavior of the magnetization and of the specific heat. Our results for the exponents of the power laws, as well as previous results for the scaling of the critical temperature to magnetic ordering with the applied field, are incompatible with the conventional crossover-scaling Ansatz proposed by Fisher [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.40.546 40, 546 (1989)]. However they can all be reconciled within a phenomenological Ansatz in the presence of a dangerously irrelevant operator.
Magnetic Quantum Tunneling in Single Molecule Magnets: Mn-12 and Others
NASA Astrophysics Data System (ADS)
del Barco, Enrique
2004-03-01
Magnetic quantum tunneling (MQT) has been studied in single molecule magnets (SMMs) using a micro-Hall effect magnetometer in a superconducting high field vector magnet system that incorporates the possibility of applying pulsed microwave fields. Mn_12-acetate has been studied extensively over the years. However, only recently the symmetry of MQT and the nature of the transverse interactions important to MQT have been determined [1,2]. Magnetic measurements in the pure quantum tunneling regime (0.6 K) illustrate that an average crystal fourfold MQT symmetry is due to local molecular environments of twofold symmetry that are rotated by 90 degrees with respect to one another, confirming that disorder which lowers the molecule symmetry is important to MQT. We have studied a subset of these lower site symmetry molecules and present evidence for a Berry phase that results from a combination of second and forth order contributions to the transverse magnetic anisotropy. These observations are consistent with high frequency EPR studies of the transverse interactions in Mn_12-acetate [3]. Finally, we discuss recent experiments in which microwave radiation is applied to modulate MQT and characterize the lifetimes and coherence times of states that are superpositions of "up" and "down" high spin-projections. [1] E. del Barco, et al., Phys. Rev. Lett. 91, 047203 (2003) [2] S. Hill, et al., Phys. Rev. Lett. 90, 217204 (2003). [3] E. del Barco, A, D. Kent, R. S. Edwards, S. I. Jones, S. Hill, J. M. North, N. S. Dalal, E. M. Rumnberger, D. N. Hendrickson and G. Christou, to be published.
Photocurrent Control in a Magnetic Field through Quantum Interference
NASA Astrophysics Data System (ADS)
Rao, Kiran Murti
Quantum-mechanical interference between excitation pathways can be used to inject photocurrents optically in semiconductors, the properties of which can be coherently controlled through the phases and polarizations of the optical pulses. In this thesis, coherent photocurrent control is investigated theoretically for two-dimensional semiconductor systems in a perpendicular magnetic field. The semiconductor systems are subjected to optical pulses with centre frequencies o 0 and 2o0, which excite interband transitions through one- and two-photon processes, selection rules for which are determined from envelope wave functions. It is shown using time-dependent perturbation theory that the interference between one- and two-photon pathways connecting a particular valence Landau level to two different but adjacent conduction Landau levels manifests itself as electron currents that rotate counterclockwise, while interference between pathways connecting two adjacent valence Landau levels to a particular conduction Landau level manifests itself as hole currents that rotate clockwise. The initial directions of the currents can be controlled by adjusting the polarizations and a relative phase parameter of the pulses. The analysis is performed for a GaAs quantum well, monolayer graphene and bilayer graphene. For GaAs, the equally spaced Landau levels in each band lead to electron currents rotating at a single frequency and hole currents rotating at a different frequency. Monolayer and bilayer graphene allow currents with multiple frequency components as well as other peculiarities resulting from additional interference processes not present for GaAs. The photocurrents in all of these systems radiate in the terahertz regime. This radiation is calculated for realistic experimental conditions, with scattering and relaxation processes accounted for phenomenologically. Finally, the effect of Coulomb interactions on the coherent control process is considered for an undoped Ga
Proposed Robust Entanglement-Based Magnetic Field Sensor Beyond the Standard Quantum Limit
NASA Astrophysics Data System (ADS)
Tanaka, Tohru; Knott, Paul; Matsuzaki, Yuichiro; Dooley, Shane; Yamaguchi, Hiroshi; Munro, William J.; Saito, Shiro
2015-10-01
Recently, there have been significant developments in entanglement-based quantum metrology. However, entanglement is fragile against experimental imperfections, and quantum sensing to beat the standard quantum limit in scaling has not yet been achieved in realistic systems. Here, we show that it is possible to overcome such restrictions so that one can sense a magnetic field with an accuracy beyond the standard quantum limit even under the effect of decoherence, by using a realistic entangled state that can be easily created even with current technology. Our scheme could pave the way for the realizations of practical entanglement-based magnetic field sensors.
Proposed Robust Entanglement-Based Magnetic Field Sensor Beyond the Standard Quantum Limit.
Tanaka, Tohru; Knott, Paul; Matsuzaki, Yuichiro; Dooley, Shane; Yamaguchi, Hiroshi; Munro, William J; Saito, Shiro
2015-10-23
Recently, there have been significant developments in entanglement-based quantum metrology. However, entanglement is fragile against experimental imperfections, and quantum sensing to beat the standard quantum limit in scaling has not yet been achieved in realistic systems. Here, we show that it is possible to overcome such restrictions so that one can sense a magnetic field with an accuracy beyond the standard quantum limit even under the effect of decoherence, by using a realistic entangled state that can be easily created even with current technology. Our scheme could pave the way for the realizations of practical entanglement-based magnetic field sensors.
Shevchenko, A B; Barabash, M Yu
2015-12-01
It is shown that at low temperatures, quantum oscillations of nanoscale structural inhomogeneities (the vertical Bloch line and the Bloch point) occur in the domain walls of cylindrical magnetic domains formed in a uniaxial magnetic film with strong magnetic anisotropy. The conditions for the excitation of these oscillations are determined.
Illustrating the quantum approach with an Earth magnetic field MRI
NASA Astrophysics Data System (ADS)
Pars Benli, Kami; Dillmann, Baudouin; Louelh, Ryma; Poirier-Quinot, Marie; Darrasse, Luc
2015-05-01
Teaching imaging of magnetic resonance (MR) today is still as challenging as it has always been, because it requires admitting that we cannot express fundamental questions of quantum mechanics with straightforward language or without using extensive theory. Here we allow students to face a real MR setup based on the Earth's magnetic field. We address the applied side of teaching MR using a device that is affordable and that proves to be sufficiently robust, at universities in Orsay, France, and San Sebastian, Spain, in experimental practicals at undergraduate and graduate levels. We specifically present some of the advantages of low field for measuring R2 relaxation rates, reaching a power of separation of 1.5 μmol on Mn(II) ions between two water bottles each of half a liter. Finally we propose key approaches for the lecturers to adopt when they are asked to pass from theoretical knowledge to teachable knowhow. The outcomes are fast calibration and the MR acquisition protocols, demonstrating the reproducibility of energy transfer during the saturation pulses, and the quantitative nature of MR, with water protons and a helium-3 sample.
Quantum Monte Carlo calculations of magnetic couplings in cuprates
NASA Astrophysics Data System (ADS)
Foyevtsova, Kateryna; Krogel, Jaron; Kim, Jeongnim; Reboredo, Fernando
2014-03-01
Spin excitations are generally believed to play a fundamental role in the mechanism of high temperature superconductivity in cuprates. However, accurate description of the cuprates' magnetic properties and, in particular, calculation of spin exchange couplings have been a long-standing challenge to the electronic structure theory. While the quantum-mechanically more rigorous cluster methods suffer from finite-size effects, the density functional theory approach, on the other hand, is ambiguous due to a rich variety of approximations to the exchange-correlation functional available which often give very different numbers for the spin exchange constants. For example, in some cuprates the theoretically predicted values of the nearest-neighbor superexchange range from 1 eV (local density approximation) to 0.05 eV (periodic unrestricted Hartree Fock) [C. de Graaf et al, PRB 63 014404 (2000)]. We compute spin exchange constants with the fixed-node diffusion Monte Carlo method (FN-DMC). In one-dimensional cuprates, we find that the FN-DMC computed nearest-neighbor spin superexchange is in an excellent agreement with experiment. This both demonstrates that FN-DMC is capable of describing properly the magnetism of strongly correlated oxides as well as positions this technique as the method of choice for theoretical parameterization of spin models. Research supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division.
Enhancement of Quantum Efficiency of Organic Light Emitting Devices by Doping Magnetic Nanoparticles
Sun, Chengjun; Wu, Yue; Xu, Zhihua; Hu, Bin; Bai, Jianmin; Wang, Jian-Ping; Shen, Jian
2007-01-01
Magnetic nanoparticles of CoFe are used as dopants to enhance the quantum efficiency of electroluminance in a single layer organic light emitting device (OLED). The enhancement of quantum efficiency increases with both increasing density of CoFe nanoparticles and external magnetic field. For a given OLED with 0.1 wt % doping, the enhancement of the quantum efficiency reaches {approx}27% and {approx}32% without and with a magnetic field, respectively. The origin of these improvements could be attributed to the simultaneous increases of the portion of excitons among total charge carriers and the fraction of singlets among the total excitons
Quantum aspects of a moving magnetic quadrupole moment interacting with an electric field
Fonseca, I. C.; Bakke, K.
2015-06-15
The quantum dynamics of a moving particle with a magnetic quadrupole moment that interacts with electric and magnetic fields is introduced. By dealing with the interaction between an electric field and the magnetic quadrupole moment, it is shown that an analogue of the Coulomb potential can be generated and bound state solutions can be obtained. Besides, the influence of the Coulomb-type potential on the harmonic oscillator is investigated, where bound state solutions to both repulsive and attractive Coulomb-type potentials are achieved and the arising of a quantum effect characterized by the dependence of the harmonic oscillator frequency on the quantum numbers of the system is discussed.
Bethe-Salpeter equation for quantum-well exciton states in an inhomogeneous magnetic field
NASA Astrophysics Data System (ADS)
Koinov, Z. G.; Nash, P.; Witzel, J.
2003-04-01
The trapping of excitons in a single quantum well due to the presence of a strong homogeneous magnetic field and a weak inhomogeneous cylindrical symmetric magnetic field, created by the deposition of a magnetized disk on top of the quantum well, both applied perpendicular to the x-y plane of confinement is studied theoretically. The numerical calculations are performed for GaAs/AlxGa1-xAs quantum wells and the formation of bound exciton states with nonzero values for the center-of-mass exciton wave function only in a small area is predicted.
Magnetic quantum phase diagram of magnetic impurities in two-dimensional disordered electron systems
NASA Astrophysics Data System (ADS)
Lee, Hyun Yong; Kettemann, Stefan
2014-04-01
The quantum phase diagram of disordered electron systems as a function of the concentration of magnetic impurities nm and the local exchange coupling J is studied in the dilute limit. We take into account the Anderson localization of the electrons by a nonperturbative numerical treatment of the disorder potential. The competition between Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction JRKKY and the Kondo effect, as governed by the temperature scale TK, is known to give rise to a rich magnetic quantum phase diagram, the Doniach diagram. Our numerical calculations show that in a disordered system both the Kondo temperature TK and JRKKY as well as their ratio JRKKY/TK is widely distributed. However, we find a sharp cutoff of that distribution, which allows us to define a critical density of magnetic impurities nc below which Kondo screening wins at all sites of the system above a critical coupling Jc, forming the Kondo phase [see Fig. 3(b)]. As disorder is increased, Jc increases and a spin coupled phase is found to grow at the expense of the Kondo phase. From these distribution functions we derive the magnetic susceptibility which show anomalous power-law behavior. In the Kondo phase that power is determined by the wide distribution of the Kondo temperature, while in the spin coupled phase it is governed by the distribution of JRKKY. At low densities and small J
Sharma, Prerana; Chhajlani, R. K.
2014-03-15
The effect of spin induced magnetization and electrical resistivity incorporating the viscosity of the medium is examined on the Jeans instability of quantum magnetoplasma. Formulation of the system is done by using the quantum magnetohydrodynamic model. The analysis of the problem is carried out by normal mode analysis theory. The general dispersion relation is derived from set of perturbed equations to analyse the growth rate and condition of self-gravitational Jeans instability. To discuss the influence of resistivity, magnetization, and viscosity parameters on Jeans instability, the general dispersion relation is reduced for both transverse and longitudinal mode of propagations. In the case of transverse propagation, the gravitating mode is found to be affected by the viscosity, magnetization, resistivity, and magnetic field strength whereas Jeans criterion of instability is modified by the magnetization and quantum parameter. In the longitudinal mode of propagation, the gravitating mode is found to be modified due to the viscosity and quantum correction in which the Jeans condition of instability is influenced only by quantum parameter. The other non-gravitating Alfven mode in this direction is affected by finite electrical resistivity, spin induced magnetization, and viscosity. The numerical study for the growth rate of Jeans instability is carried out for both in the transverse and longitudinal direction of propagation to the magnetic field. The effect of various parameters on the growth rate of Jeans instability in quantum plasma is analysed.
NASA Astrophysics Data System (ADS)
Cruz, C.; Soares-Pinto, D. O.; Brandão, P.; dos Santos, A. M.; Reis, M. S.
2016-02-01
The control of quantum correlations in solid-state systems by means of material engineering is a broad avenue to be explored, since it makes possible steps toward the limits of quantum mechanics and the design of novel materials with applications on emerging quantum technologies. In this context, this letter explores the potential of molecular magnets to be prototypes of materials for quantum information technology. More precisely, we engineered a material and from its geometric quantum discord we found significant quantum correlations up to 9540 K (even without entanglement); and, in addition, a pure singlet state occupied up to around 80 K (above liquid nitrogen temperature). These results could only be achieved due to the carboxylate group promoting a metal-to-metal huge magnetic interaction.
Digital quantum simulation of the statistical mechanics of a frustrated magnet.
Zhang, Jingfu; Yung, Man-Hong; Laflamme, Raymond; Aspuru-Guzik, Alán; Baugh, Jonathan
2012-06-06
Many problems of interest in physics, chemistry and computer science are equivalent to problems defined on systems of interacting spins. However, most such problems require computational resources that are out of reach with classical computers. A promising solution to overcome this challenge is quantum simulation. Several 'analogue' quantum simulations of interacting spin systems have been realized experimentally, where ground states were prepared using adiabatic techniques. Here we report a 'digital' quantum simulation of thermal states; a three-spin frustrated magnet was simulated using a nuclear magnetic resonance quantum information processor, and we were able to explore the phase diagram of the system at any simulated temperature and external field. These results help to identify the challenges for performing quantum simulations of physical systems at finite temperatures, and suggest methods that may be useful in simulating thermal open quantum systems.
Val’kov, V. V. Shustin, M. S.
2015-11-15
The dispersion equation of a strongly anisotropic one-dimensional magnet catena-[Fe{sup II}(ClO{sub 4}){sub 2}(Fe{sup III}(bpca){sub 2})]ClO{sub 4} containing alternating high-spin (HS) (S = 2) and low-spin (LS) (S = 1/2) iron ions is obtained by the diagram technique for Hubbard operators. The analysis of this equation yields six branches in the excitation spectrum of this magnet. It is important that the crystal field for ions with spin S = 2 is described by the Hamiltonian of single-ion easy-plane anisotropy, whose orientation is changed by 90° when passing from one HS iron ion to another. The U(N) transformation technique in the atomic representation is applied to diagonalize a single-ion Hamiltonian with a large number of levels. It is shown that the modulation of the orientation of easy magnetization planes leads to a model of a ferrimagnet with easy-axis anisotropy and to the formation of energy spectrum with a large gap. For HS iron ions, a decrease in the mean value of the spin projection due to quantum fluctuations is calculated. The analysis of the specific features of the spectrum of elementary excitations allows one to establish a correspondence to a generalized Ising model for which the magnetic susceptibility is calculated in a wide range of temperatures by the transfer-matrix method. The introduction of a statistical ensemble that takes into account the presence of chains of different lengths and the presence of iron ions with different spins allows one to describe the experimentally observed modification of the magnetic susceptibility of the magnet under optical irradiation.
NASA Astrophysics Data System (ADS)
Haas, Fernando; Mahmood, Shahzad
2016-09-01
Nonlinear ion-acoustic waves are analyzed in a nonrelativistic magnetized quantum plasma with arbitrary degeneracy of electrons. Quantum statistics is taken into account by means of the equation of state for ideal fermions at arbitrary temperature. Quantum diffraction is described by a modified Bohm potential consistent with finite-temperature quantum kinetic theory in the long-wavelength limit. The dispersion relation of the obliquely propagating electrostatic waves in magnetized quantum plasma with arbitrary degeneracy of electrons is obtained. Using the reductive perturbation method, the corresponding Zakharov-Kuznetsov equation is derived, describing obliquely propagating two-dimensional ion-acoustic solitons in a magnetized quantum plasma with degenerate electrons having an arbitrary electron temperature. It is found that in the dilute plasma case only electrostatic potential hump structures are possible, while in dense quantum plasma, in principle, both hump and dip soliton structures are obtainable, depending on the electron plasma density and its temperature. The results are validated by comparison with the quantum hydrodynamic model including electron inertia and magnetization effects. Suitable physical parameters for observations are identified.
NASA Astrophysics Data System (ADS)
Engelhardt, Larry
2015-12-01
We discuss how computers can be used to solve the ordinary differential equations that provide a quantum mechanical description of magnetic resonance. By varying the parameters in these equations and visually exploring how these parameters affect the results, students can quickly gain insights into the nature of magnetic resonance that go beyond the standard presentation found in quantum mechanics textbooks. The results were generated using an IPython notebook, which we provide as an online supplement with interactive plots and animations.
NASA Astrophysics Data System (ADS)
Ruan, Shi-Sen; Wu, Shan; Raissan, Majid; Cheng, Ze
2013-08-01
This article presents the first study of the head-on collision between two magnetoacoustic solitary waves (MASWs) in magnetized quantum plasma consisting of electrons, positrons, and ions, using the extended Poincaré-Lighthill-Kou (PLK) method. The effects of the magnetic field intensity, the positron to ion number density ratio, the quantum parameter, the Fermi temperature ratio, and plasma number density on the solitary wave collisions are investigated. It is shown that these factors significantly modify the phase shift.
Magnetic properties and the effect of non-magnetic impurities in the quasi-2D quantum magnet
NASA Astrophysics Data System (ADS)
Khuntia, P.; Dey, T.; Mahajan, A. V.
2016-09-01
We present synthesis, x-ray diffraction, magnetisation and specific heat studies on the quasi-two-dimensional (2D) S = 1/2 antiferromagnet (CuCl)LaNb2O7 and its doping analogues (Cu1-x Zn x Cl)LaNb2O7 (0 ≤ x ≤ 0.05), (Cu0.95Mg0.05Cl)LaNb2O7, and (CuCl)La1-y Ba y Nb2O7 (0 ≤ y ≤ 0.10). The magnetic susceptibility and specific heat of the parent compound and its isovalent or hetereovalent counterparts do not display any signature of magnetic ordering down to 1.8 K. The parent compound and its doping variants exhibit spin-singlet behaviour with a finite gap in the spin excitation spectrum due to dimerisation of the dominant intradimer interactions as evidenced from our magnetic susceptibility and specific heat data. The systematic increase of magnetic susceptibility at low temperature with non-magnetic Zn2+ and Mg2+ (S = 0) substitution at the Cu2+ site reflect that impurities induce local moments around the non-magnetic sites. While heterovalent Ba2+ substitution at the La3+ site do not result in mobile holes but rather give rise to a Curie term in the susceptibility due to localisation. The low value of spin S = 1/2, and absence of long range ordering or spin freezing, and the presence of competing exchange interactions hold special significance in hosting novel magnetic properties in this class of quasi-2D quantum material.
Magnetic properties and the effect of non-magnetic impurities in the quasi-2D quantum magnet
NASA Astrophysics Data System (ADS)
Khuntia, P.; Dey, T.; Mahajan, A. V.
2016-09-01
We present synthesis, x-ray diffraction, magnetisation and specific heat studies on the quasi-two-dimensional (2D) S = 1/2 antiferromagnet (CuCl)LaNb2O7 and its doping analogues (Cu1‑x Zn x Cl)LaNb2O7 (0 ≤ x ≤ 0.05), (Cu0.95Mg0.05Cl)LaNb2O7, and (CuCl)La1‑y Ba y Nb2O7 (0 ≤ y ≤ 0.10). The magnetic susceptibility and specific heat of the parent compound and its isovalent or hetereovalent counterparts do not display any signature of magnetic ordering down to 1.8 K. The parent compound and its doping variants exhibit spin-singlet behaviour with a finite gap in the spin excitation spectrum due to dimerisation of the dominant intradimer interactions as evidenced from our magnetic susceptibility and specific heat data. The systematic increase of magnetic susceptibility at low temperature with non-magnetic Zn2+ and Mg2+ (S = 0) substitution at the Cu2+ site reflect that impurities induce local moments around the non-magnetic sites. While heterovalent Ba2+ substitution at the La3+ site do not result in mobile holes but rather give rise to a Curie term in the susceptibility due to localisation. The low value of spin S = 1/2, and absence of long range ordering or spin freezing, and the presence of competing exchange interactions hold special significance in hosting novel magnetic properties in this class of quasi-2D quantum material.
Analytical method for determining quantum well exciton properties in a magnetic field
NASA Astrophysics Data System (ADS)
Stépnicki, Piotr; Piétka, Barbara; Morier-Genoud, François; Deveaud, Benoît; Matuszewski, Michał
2015-05-01
We develop an analytical approximate method for determining the Bohr radii of Wannier-Mott excitons in thin quantum wells under the influence of magnetic field perpendicular to the quantum well plane. Our hybrid variational-perturbative method allows us to obtain simple closed formulas for exciton binding energies and optical transition rates. We confirm the reliability of our method through exciton-polariton experiments realized in a GaAs/AlAs microcavity with an 8 nm InxGa1 -xAs quantum well and magnetic field strengths as high as 14 T.
Temporal Behavior of Radiation-Pressure-Induced Vibrations of an Optical Microcavity Phonon Mode
NASA Astrophysics Data System (ADS)
Carmon, Tal; Rokhsari, Hossein; Yang, Lan; Kippenberg, Tobias J.; Vahala, Kerry J.
2005-06-01
We analyze experimentally and theoretically mechanical oscillation within an optical cavity stimulated by the pressure of circulating optical radiation. The resulting radio frequency cavity vibrations (phonon mode) cause modulation of the incident, continuous-wave (cw) input pump beam. Furthermore, with increasing cw pump power, an evolution from sinusoidal modulation to random oscillations is observed in the pump power coupled from the resonator. The temporal evolution with pump power is studied, and agreement was found with theory. In addition to applications in quantum optomechanics, the present work suggests that radiation-pressure-induced effects can establish a practical limit for the miniaturization of optical silica microcavities.
Omidi, Mahboubeh Faizabadi, Edris
2015-03-21
Magnetic susceptibility is investigated in a man-made elliptical quantum ring in the presence of Rashba spin-orbit interactions and the magnetic flux. It is shown that magnetic susceptibility as a function of magnetic flux changes between negative and positive signs periodically. The periodicity of the Aharonov-Bohm oscillations depends on the geometry of the region where magnetic field is applied, the eccentricity, and number of sites in each chain ring (the elliptical ring is composed of chain rings). The magnetic susceptibility sign can be reversed by tuning the Rashba spin-orbit strength as well. Both the magnetic susceptibility strength and sign can be controlled via external spin-orbit interactions, which can be exploited in spintronics and nanoelectronics.
Pressure-induced superconductivity in europium metal
Debessai, M.; Matsuoka, T.; Hamlin, J.J.; Bi, W.; Meng, Y.; Shimizu, K.; Schilling, J.S.
2010-05-24
Of the 52 known elemental superconductors among the 92 naturally occurring elements in the periodic table, fully 22 only become superconducting under sufficiently high pressure. In the rare-earth metals, the strong local magnetic moments originating from the 4f shell suppress superconductivity. For Eu, however, Johansson and Rosengren have suggested that sufficiently high pressures should promote one of its 4f electrons into the conduction band, changing Eu from a strongly magnetic (J=7/2) 4f{sup 7}-state into a weak Van Vleck paramagnetic (J=0) 4f{sup 6}-state, thus opening the door for superconductivity, as in Am (5f{sup 6}). We report that Eu becomes superconducting above 1.8 K for pressures exceeding 80 GPa, T{sub c} increasing linearly with pressure to 142 GPa at the rate +15 mK/GPa. Eu thus becomes the 53rd elemental superconductor in the periodic table. Synchrotron x-ray diffraction studies to 92 GPa at ambient temperature reveal four structural phase transitions.
Group velocity of extraordinary waves in superdense magnetized quantum plasma with spin-1/2 effects
NASA Astrophysics Data System (ADS)
Li, Chunhua; Wu, Zhengwei; Ren, Haijun; Yang, Weihong; Chu, Paul K.
2012-12-01
Based on the one component plasma model, a new dispersion relation and group velocity of elliptically polarized extraordinary electromagnetic waves in a superdense quantum magnetoplasma are derived. The group velocity of the extraordinary wave is modified due to the quantum forces and magnetization effects within a certain range of wave numbers. It means that the quantum spin-1/2 effects can reduce the transport of energy in such quantum plasma systems. Our work should be of relevance for the dense astrophysical environments and the condensed matter physics.
Group velocity of extraordinary waves in superdense magnetized quantum plasma with spin-1/2 effects
Li Chunhua; Ren Haijun; Yang Weihong; Wu Zhengwei; Chu, Paul K.
2012-12-15
Based on the one component plasma model, a new dispersion relation and group velocity of elliptically polarized extraordinary electromagnetic waves in a superdense quantum magnetoplasma are derived. The group velocity of the extraordinary wave is modified due to the quantum forces and magnetization effects within a certain range of wave numbers. It means that the quantum spin-1/2 effects can reduce the transport of energy in such quantum plasma systems. Our work should be of relevance for the dense astrophysical environments and the condensed matter physics.
Using thermal boundary conditions to engineer the quantum state of a bulk magnet
Schmidt, M. A.; Silevitch, D. M.; Aeppli, G.; Rosenbaum, T. F.
2014-01-01
The degree of contact between a system and the external environment can alter dramatically its proclivity to quantum mechanical modes of relaxation. We show that controlling the thermal coupling of cubic-centimeter–sized crystals of the Ising magnet LiHoxY1-xF4 to a heat bath can be used to tune the system between a glassy state dominated by thermal excitations over energy barriers and a state with the hallmarks of a quantum spin liquid. Application of a magnetic field transverse to the Ising axis introduces both random magnetic fields and quantum fluctuations, which can retard and speed the annealing process, respectively, thereby providing a mechanism for continuous tuning between the destination states. The nonlinear response of the system explicitly demonstrates quantum interference between internal and external relaxation pathways. PMID:24567389
Using thermal boundary conditions to engineer the quantum state of a bulk magnet.
Schmidt, M A; Silevitch, D M; Aeppli, G; Rosenbaum, T F
2014-03-11
The degree of contact between a system and the external environment can alter dramatically its proclivity to quantum mechanical modes of relaxation. We show that controlling the thermal coupling of cubic-centimeter-sized crystals of the Ising magnet LiHo(x)Y(1-x)F4 to a heat bath can be used to tune the system between a glassy state dominated by thermal excitations over energy barriers and a state with the hallmarks of a quantum spin liquid. Application of a magnetic field transverse to the Ising axis introduces both random magnetic fields and quantum fluctuations, which can retard and speed the annealing process, respectively, thereby providing a mechanism for continuous tuning between the destination states. The nonlinear response of the system explicitly demonstrates quantum interference between internal and external relaxation pathways. PMID:24567389
Exact scattering matrix of graphs in magnetic field and quantum noise
Caudrelier, Vincent; Mintchev, Mihail; Ragoucy, Eric
2014-08-15
We consider arbitrary quantum wire networks modelled by finite, noncompact, connected quantum graphs in the presence of an external magnetic field. We find a general formula for the total scattering matrix of the network in terms of its local scattering properties and its metric structure. This is applied to a quantum ring with N external edges. Connecting the external edges of the ring to heat reservoirs, we study the quantum transport on the graph in ambient magnetic field. We consider two types of dynamics on the ring: the free Schrödinger and the free massless Dirac equations. For each case, a detailed study of the thermal noise is performed analytically. Interestingly enough, in presence of a magnetic field, the standard linear Johnson-Nyquist law for the low temperature behaviour of the thermal noise becomes nonlinear. The precise regime of validity of this effect is discussed and a typical signature of the underlying dynamics is observed.
Tightly bound 3D quantum dot energy states in a magnetic field
NASA Astrophysics Data System (ADS)
Morgenstern Horing, Norman J.; Liu, S. Y.; Sawamura, M.
2010-01-01
We have analyzed the detailed quantum dynamics of a 3D quantum dot in a magnetic field. The dot is taken to be lodged in a bulk medium in a high magnetic field and it is represented by a three-dimensional Dirac delta function potential which would support just one subband state if there were no magnetic field. The integral equation for the Schrödinger Green's function of this system is solved in closed form analytically and the single particle subband energy spectrum and the density of states are examined taking account of splintering of the subband spectrum by landau quantization.
Influence of external magnetic field on dynamics of open quantum systems
Kalandarov, Sh. A.; Kanokov, Z.; Adamian, G. G.; Antonenko, N. V.
2007-03-15
The influence of an external magnetic field on the non-Markovian dynamics of an open two-dimensional quantum system is investigated. The fluctuations of collective coordinate and momentum and transport coefficients are studied for a charged harmonic oscillator linearly coupled to a neutral bosonic heat bath. It is shown that the dissipation of collective energy slows down with increasing strength of the external magnetic field. The role of magnetic field in the diffusion processes is illustrated by several examples.
Exchange interaction and oscillations of the magnetization of the electron gas in a quantum cylinder
Eminov, P. A. Sezonov, Yu. I.; Al'pern, A. V.; Sal'nikov, N. V.
2006-10-15
The exchange energy of the electron gas on a cylindrical surface in a constant magnetic field has been calculated. Analytical formulas describing the contribution of the exchange interaction into oscillations of the magnetization of the electron gas in a quantum cylinder have been obtained. It is shown that the magnetic response of the system exhibits Aharonov-Bohm oscillations for both degenerate and Boltzmann electron gases.
Kuroda, Kagayaki; Shirakawa, Naoki; Yoshida, Yoshiyuki; Tawara, Kazuya; Kobayashi, Akihiro; Nakai, Toshiharu
2014-01-01
We evaluated the magnetization of 21 cosmetic contact lens samples that included various coloring materials with a superconducting quantum interference device with regard to magnetic resonance (MR) safety. We found 7 samples were ferromagnetic; two had both ferromagnetic and diamagnetic properties; and the rest were diamagnetic. The saturated magnetization of the most ferromagnetic sample was 15.0 µJ/T, which yielded a magnetically induced displacement force of 90.0 µN when the spatial gradient of the static magnetic field was 6.0 T/m. The force was less than one-third of the gravitational force.
Karpman-Washimi magnetization with electron-exchange effects in quantum plasmas
Hong, Woo-Pyo; Jamil, M.; Rasheed, A.; Jung, Young-Dae
2015-07-15
The influence of quantum electron-exchange on the Karpman-Washimi ponderomotive magnetization is investigated in quantum plasmas. The ponderomotive magnetization and the total radiation power due to the non-stationary Karpman-Washimi interaction related to the time-varying field intensity are obtained as functions of the de Broglie wave length, Debye length, and electron-exchange parameter. The result shows that the electron-exchange effect enhances the cyclotron frequency due to the ponderomotive interactions in quantum plasmas. It is also shown that the electron-exchange effect on the Karpman-Washimi magnetization increases with increasing wave number. In addition, the Karpman-Washimi magnetization and the total radiation power increase with an increase in the ratio of the Debye length to the de Broglie wave length. In streaming quantum plasmas, it is shown that the electron-exchange effect enhances the ponderomotive magnetization below the resonant wave number and, however, suppresses the ponderomotive magnetization above the resonant wave number. The variation of the Karpman-Washimi magnetization and the radiation power due to the variation of the electron-exchange effect and plasma parameters is also discussed.
Low-temperature heat transport of spin-gapped quantum magnets
NASA Astrophysics Data System (ADS)
Zhao, Xia; Zhao, ZhiYing; Liu, XuGuang; Sun, XueFeng
2016-11-01
This article reviews low-temperature heat transport studies of spin-gapped quantum magnets in the last few decades. Quantum magnets with small spins and low dimensionality exhibit a variety of novel phenomena. Among them, some systems are characteristic of having quantum-mechanism spin gap in their magnetic excitation spectra, including spin-Peierls systems, S=1 Haldane chains, S= 1/2 spin ladders, and spin dimmers. In some particular spin-gapped systems, the XY-type antiferromagnetic state induced by magnetic field that closes the spin gap can be described as a magnon Bose-Einstein condensation (BEC). Heat transport is effective in probing the magnetic excitations and magnetic phase transitions, and has been extensively studied for the spin-gapped systems. A large and ballistic spin thermal conductivity was observed in the two-leg Heisenberg S=1/2 ladder compounds. The characteristic of magnetic thermal transport of the Haldane chain systems is quite controversial on both the theoretical and experimental results. For the spin-Peierls system, the spin excitations can also act as heat carriers. In spin-dimer compounds, the magnetic excitations mainly play a role of scattering phonons. The magnetic excitations in the magnon BEC systems displayed dual roles, carrying heat or scattering phonons, in different materials.
NASA Astrophysics Data System (ADS)
Faizabadi, Edris; Eslami, Leila
2012-06-01
The influence of quantum dot magnetization on electronic spin-dependent transport is investigated through a triple-quantum-dot ring structure in which one of the quantum dots is non-magnetic subjected to the Rashba spin-orbit interaction and the two other ones possess magnetic structure. Evaluated results, based on single particle Green's function formalism, indicate that the presence of magnetic moment on the quantum dots leads to additional spin-dependent phase factor which affects electronic transport through the system. For both antiferromagnetic and ferromagnetic quantum dots, the system can operate as a spin-splitter but differently; by tuning Rashba spin-orbit strength and in the presence of magnetic flux, respectively. Besides, in the absence of one of the outgoing leads, spin current in the output is calculated and demonstrated that magnetization of quantum dots leads to spin current even in the absence of Rashba spin-orbit effect. Moreover, it is shown that in the presence of Rashba spin orbit interaction, magnetic quantum dots, and magnetic flux, the two terminal system produces a completely tunable spin current.
Longitudinal wave function control in single quantum dots with an applied magnetic field.
Cao, Shuo; Tang, Jing; Gao, Yunan; Sun, Yue; Qiu, Kangsheng; Zhao, Yanhui; He, Min; Shi, Jin-An; Gu, Lin; Williams, David A; Sheng, Weidong; Jin, Kuijuan; Xu, Xiulai
2015-01-01
Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots. PMID:25624018
Field-induced magnetization jumps and quantum criticality in the 2D J-Q model
NASA Astrophysics Data System (ADS)
Iaizzi, Adam; Sandvik, Anders
The J-Q model is a `designer hamiltonian' formed by adding a four spin `Q' term to the standard antiferromagnetic S = 1 / 2 Heisenberg model. The Q term drives a quantum phase transition to a valence-bond solid (VBS) state: a non-magnetic state with a pattern of local singlets which breaks lattice symmetries. The elementary excitations of the VBS are triplons, i.e. gapped S=1 quasiparticles. There is considerable interest in the quantum phase transition between the Néel and VBS states as an example of deconfined quantum criticality. Near the phase boundary, triplons deconfine into pairs of bosonic spin-1/2 excitations known as spinons. Using exact diagonalization and the stochastic series expansion quantum monte carlo method, we study the 2D J-Q model in the presence of an external magnetic field. We use the field to force a nonzero density of magnetic excitations at T=0 and look for signatures of Bose-Einstein condensation of spinons. At higher magnetic fields, there is a jump in the induced magnetization caused by the onset of an effective attractive interaction between magnons on a ferromagnetic background. We characterize the first order quantum phase transition and determine the minimum value of the coupling ratio q ≡ Q / J required to produce this jump. Funded by NSF DMR-1410126.
Longitudinal wave function control in single quantum dots with an applied magnetic field
Cao, Shuo; Tang, Jing; Gao, Yunan; Sun, Yue; Qiu, Kangsheng; Zhao, Yanhui; He, Min; Shi, Jin-An; Gu, Lin; Williams, David A.; Sheng, Weidong; Jin, Kuijuan; Xu, Xiulai
2015-01-01
Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots. PMID:25624018
Magnetic field induced optical gain in a dilute nitride quaternary semiconductor quantum dot
NASA Astrophysics Data System (ADS)
Mageshwari, P. Uma; Peter, A. John; Lee, Chang Woo
2016-10-01
Effects of magnetic field strength on the electronic and optical properties are brought out in a Ga0.661In0.339N0.0554As0.9446/GaAs quantum dot for the applications of desired wavelength in opto-electronic devices. The band alignment is obtained using band anticrossing model and the model solid theory. The magnetic field dependent electron-heavy hole transition energies with the dot radius in a GaInNAs/GaAs quantum dot are investigated. The magnetic field induced oscillator strength as a function of dot radius is studied. The resonant peak values of optical absorption coefficients and the changes of refractive index with the application of magnetic field strength in a GaInNAs/GaAs quantum dot are obtained. The magnetic field induced threshold current density and the maximum optical gain are found in a GaInNAs/GaAs quantum dot. The results show that the optimum wavelength for fibre optical communication networks can be obtained with the variation of applied magnetic field strength and the outcomes may be useful for the design of efficient lasers based on the group III-N-V semiconductors.
Magnetic transitions and quantum criticality in the three-dimensional Hubbard model
NASA Astrophysics Data System (ADS)
Schäfer, Thomas; Katanin, Andrey; Held, Karsten; Toschi, Alessandro
We analyze the (quantum) critical properties of the simplest model for electronic correlations, the Hubbard model, in three spatial dimensions by means of the dynamical mean field theory (DMFT, including all local correlations) and the dynamical vertex approximation (D ΓA, including non-local correlations on all length scales). Both in the half-filled/unfrustrated and in the hole-doped system the transition temperature is significantly lowered by including non-local fluctuations.In the latter case, however, the magnetic order becomes incommensurate, eventually leading to a complete suppression of the order and giving rise to a magnetic quantum critical point (QCP) at zero temperature. We analyze the (quantum) critical properties of this QCP (e.g. critical exponents) and relate our findings to the standard theory of quantum criticality in metals, the Hertz-Millis-Moriya theory. Solids4Fun, Austrian Science Fund (FWF, Project ID 1243).
Jeans instability of rotating magnetized quantum plasma: Influence of radiation
Joshi, H.; Pensia, R. K.
2015-07-31
The effect of radiative heat-loss function and rotation on the Jeans instability of quantum plasma is investigated. The basic set of equations for this problem is constructed by considering quantum magnetohydrodynamic (QMHD) model. Using normal mode analysis, the general dispersion relation is obtained. This dispersion relation is studied in both, longitudinal and transverse direction of propagations. In both case of longitudinal and transverse direction of propagation, the Jeans instability criterion is modified due to presence of radiative heat-loss function and quantum correction.
Low-frequency surface waves on semi-bounded magnetized quantum plasma
NASA Astrophysics Data System (ADS)
Moradi, Afshin
2016-08-01
The propagation of low-frequency electrostatic surface waves on the interface between a vacuum and an electron-ion quantum plasma is studied in the direction perpendicular to an external static magnetic field which is parallel to the interface. A new dispersion equation is derived by employing both the quantum magnetohydrodynamic and Poisson equations. It is shown that the dispersion equations for forward and backward-going surface waves are different from each other.
Dual-channel spontaneous emission of quantum dots in magnetic metamaterials.
Decker, Manuel; Staude, Isabelle; Shishkin, Ivan I; Samusev, Kirill B; Parkinson, Patrick; Sreenivasan, Varun K A; Minovich, Alexander; Miroshnichenko, Andrey E; Zvyagin, Andrei; Jagadish, Chennupati; Neshev, Dragomir N; Kivshar, Yuri S
2013-01-01
Metamaterials, artificial electromagnetic media realized by subwavelength nano-structuring, have become a paradigm for engineering electromagnetic space, allowing for independent control of both electric and magnetic responses of the material. Whereas most metamaterials studied so far are limited to passive structures, the need for active metamaterials is rapidly growing. However, the fundamental question on how the energy of emitters is distributed between both (electric and magnetic) interaction channels of the metamaterial still remains open. Here we study simultaneous spontaneous emission of quantum dots into both of these channels and define the control parameters for tailoring the quantum-dot coupling to metamaterials. By superimposing two orthogonal modes of equal strength at the wavelength of quantum-dot photoluminescence, we demonstrate a sharp difference in their interaction with the magnetic and electric metamaterial modes. Our observations reveal the importance of mode engineering for spontaneous emission control in metamaterials, paving a way towards loss-compensated metamaterials and metamaterial nanolasers.
Rauf Abdullah, Nzar; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar
2016-09-21
We investigate theoretically the balance of the static magnetic and the dynamical photon forces in the electron transport through a quantum dot in a photon cavity with a single photon mode. The quantum dot system is connected to external leads and the total system is exposed to a static perpendicular magnetic field. We explore the transport characteristics through the system by tuning the ratio, [Formula: see text], between the photon energy, [Formula: see text], and the cyclotron energy, [Formula: see text]. Enhancement in the electron transport with increasing electron-photon coupling is observed when [Formula: see text]. In this case the photon field dominates and stretches the electron charge distribution in the quantum dot, extending it towards the contact area for the leads. Suppression in the electron transport is found when [Formula: see text], as the external magnetic field causes circular confinement of the charge density around the dot.
Rauf Abdullah, Nzar; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar
2016-09-21
We investigate theoretically the balance of the static magnetic and the dynamical photon forces in the electron transport through a quantum dot in a photon cavity with a single photon mode. The quantum dot system is connected to external leads and the total system is exposed to a static perpendicular magnetic field. We explore the transport characteristics through the system by tuning the ratio, [Formula: see text], between the photon energy, [Formula: see text], and the cyclotron energy, [Formula: see text]. Enhancement in the electron transport with increasing electron-photon coupling is observed when [Formula: see text]. In this case the photon field dominates and stretches the electron charge distribution in the quantum dot, extending it towards the contact area for the leads. Suppression in the electron transport is found when [Formula: see text], as the external magnetic field causes circular confinement of the charge density around the dot. PMID:27420809
Magnetization dynamics down to a zero field in dilute (Cd,Mn)Te quantum wells.
Goryca, M; Ferrand, D; Kossacki, P; Nawrocki, M; Pacuski, W; Maślana, W; Gaj, J A; Tatarenko, S; Cibert, J; Wojtowicz, T; Karczewski, G
2009-01-30
The evolution of the magnetization in (Cd,Mn)Te quantum wells after a short pulse of magnetic field was determined from the giant Zeeman shift of spectroscopic lines. The dynamics in the absence of a static magnetic field was found to be up to 3 orders of magnitude faster than that at 1 T. Hyperfine interaction and strain are mainly responsible for the fast decay. The influence of a hole gas is clearly visible: at zero field anisotropic holes stabilize the system of Mn ions, while in a magnetic field of 1 T they are known to speed up the decay by opening an additional relaxation channel.
Murguia, Gabriela; Moreno, Matias; Torres, Manuel
2009-04-20
A well known example in quantum electrodynamics (QED) shows that Coulomb scattering of unpolarized electrons, calculated to lowest order in perturbation theory, yields a results that exactly coincides (in the non-relativistic limit) with the Rutherford formula. We examine an analogous example, the classical and perturbative quantum scattering of an electron by a magnetic field confined in an infinite solenoid of finite radius. The results obtained for the classical and the quantum differential cross sections display marked differences. While this may not be a complete surprise, one should expect to recover the classical expression by applying the classical limit to the quantum result. This turn not to be the case. Surprisingly enough, it is shown that the classical result can not be recuperated even if higher order corrections are included. To recover the classic correspondence of the quantum scattering problem a suitable non-perturbative methodology should be applied.
Critical behavior of quantum magnets with long-range interactions in the thermodynamic limit
NASA Astrophysics Data System (ADS)
Fey, Sebastian; Schmidt, Kai Phillip
2016-08-01
Quasiparticle properties of quantum magnets with long-range interactions are investigated by high-order linked-cluster expansions in the thermodynamic limit. It is established that perturbative continuous unitary transformations on white graphs are a promising and flexible approach to treat long-range interactions in quantum many-body systems. We exemplify this scheme for the one-dimensional transverse-field Ising chain with long-range interactions. For this model, the elementary quasiparticle gap is determined allowing to access the quantum-critical regime including critical exponents and multiplicative logarithmic corrections for the ferro- and antiferromagnetic case.
Band structure and itinerant magnetism in quantum critical NbFe2
Subedi, A. P.; Singh, David J
2010-01-01
We report first-principles calculations of the band structure and magnetic ordering in the C14 Laves phase compound NbFe{sub 2}. The magnetism is itinerant in the sense that the moments are highly dependent on ordering. We find an overestimation of the magnetic tendency within the local spin-density approximation, similar to other metals near magnetic quantum critical points. We also find a competition between different magnetic states due to band-structure effects. These lead to competing magnetic tendencies due to competing interlayer interactions, one favoring a ferrimagnetic solution and the other an antiferromagnetic state. While the structure contains Kagome lattice sheets, which could, in principle, lead to strong magnetic frustration, the calculations do not show dominant nearest-neighbor antiferromagnetic interactions within these sheets. These results are discussed in relation to experimental observations.
Tomimatsu, Toru Shirai, Shota; Hashimoto, Katsushi Sato, Ken; Hirayama, Yoshiro
2015-08-15
Electric-field-induced nuclear resonance (NER: nuclear electric resonance) involving quantum Hall states (QHSs) was studied at various filling factors by exploiting changes in nuclear spins polarized at quantum Hall breakdown. Distinct from the magnetic dipole interaction in nuclear magnetic resonance, the interaction of the electric-field gradient with the electric quadrupole moment plays the dominant role in the NER mechanism. The magnitude of the NER signal strongly depends on whether electronic states are localized or extended. This indicates that NER is sensitive to the screening capability of the electric field associated with QHSs.
Trapped-ion quantum logic gates based on oscillating magnetic fields.
Ospelkaus, C; Langer, C E; Amini, J M; Brown, K R; Leibfried, D; Wineland, D J
2008-08-29
Oscillating magnetic fields and field gradients can be used to implement single-qubit rotations and entangling multiqubit quantum gates for trapped-ion quantum information processing (QIP). With fields generated by currents in microfabricated surface-electrode traps, it should be possible to achieve gate speeds that are comparable to those of optically induced gates for realistic distances between the ion crystal and the electrode surface. Magnetic-field-mediated gates have the potential to significantly reduce the overhead in laser-beam control and motional-state initialization compared to current QIP experiments with trapped ions and will eliminate spontaneous scattering, a fundamental source of decoherence in laser-mediated gates.
Zhou Weihang; Chen Zhanghai; Zhang Bo; Yu, C. H.; Lu Wei; Shen, S. C.
2010-07-09
We report magnetic field control of the quantum chaotic dynamics of hydrogen analogues in an anisotropic solid state environment. The chaoticity of the system dynamics was quantified by means of energy level statistics. We analyzed the magnetic field dependence of the statistical distribution of the impurity energy levels and found a smooth transition between the Poisson limit and the Wigner limit, i.e., transition between regular Poisson and fully chaotic Wigner dynamics. The effect of the crystal field anisotropy on the quantum chaotic dynamics, which manifests itself in characteristic transitions between regularity and chaos for different field orientations, was demonstrated.
Electromagnetic drift waves in nonuniform quantum magnetized electron positron ion plasmas
NASA Astrophysics Data System (ADS)
Ren, Haijun; Wu, Zhengwei; Cao, Jintao; Chu, Paul K.
2008-03-01
Electromagnetic drift waves in a nonuniform quantum magnetized electron positron ion (EPI) plasma are studied. By using the quantum hydrodynamic equations with magnetic fields of the Wigner Maxwell system, we obtained a new dispersion relation in which ions' motions are not considered. The positrons component (featured by the parameter ξ), density gradient of electrons, and of positrons are shown to have a significant impact on the dispersion relation. Our results should be relevant to dense astrophysical objects, e.g. white dwarf and pulsar magnetospheres, as well as low-temperature laboratory EPI plasmas.
Dipolar polaritons in microcavity-embedded coupled quantum wells in electric and magnetic fields
NASA Astrophysics Data System (ADS)
Wilkes, J.; Muljarov, E. A.
2016-09-01
We present a microscopic calculation of spatially indirect exciton states in semiconductor coupled quantum wells and polaritons formed from their coupling to the optical mode of a microcavity. We include the presence of electric and magnetic fields applied perpendicular to the quantum well plane. Our model predicts the existence of polaritons that are in the strong-coupling regime and at the same time possess a large static dipole moment. We demonstrate, in particular, that a magnetic field can compensate for the reduction in light-matter coupling that occurs when an electric field impresses a dipole moment on the polariton.
Prajapati, R. P.
2014-11-15
In this work, the low frequency waves and gravitational (Jeans) instability of a homogeneous gyrotropic, magnetized, quantum plasma is investigated using the quantum magnetohydrodynamic and Chew-Goldberger-Low fluid models. An analytical dispersion relation for the considered system is obtained solving the linearized perturbations equations employing the Fourier transformation. The onset criterion of the “firehose” instability is retained in parallel propagation, which is unaffected due to the presence of quantum corrections. The gravitational mode modified by the quantum corrections is obtained separately along with the “firehose” mode. In perpendicular propagation, the quantum diffraction term is coupled with the Jeans and Alfven modes whereas in parallel propagation, the Alfven mode does not contribute to the dispersion characteristics as it leads to the “firehose” instability criterion in terms of quantum pressure anisotropy. The stabilizing influences of the quantum diffraction parameter and magnetic field on the growth rates of Jeans instability are examined. It is observed that the growth rate stabilizes much faster in transverse mode due to Alfven stabilization as compared to the longitudinal mode of propagation.
Field-induced magnetic instability and quantum criticality in the antiferromagnet CeCu2Ge2
NASA Astrophysics Data System (ADS)
Liu, Yi; Xie, Donghua; Wang, Xiaoying; Zhu, Kangwei; Yang, Ruilong
2016-01-01
The magnetic quantum criticality in strongly correlated electron systems has been considered to be closely related with the occurrence of unconventional superconductivity. Control parameters such as magnetic field, pressure or chemical doping are frequently used to externally tune the quantum phase transition for a deeper understanding. Here we report the research of a field-induced quantum phase transition using conventional bulk physical property measurements in the archetypal antiferromagnet CeCu2Ge2, which becomes superconductive under a pressure of about 10 GPa with Tc ~ 0.64 K. We offer strong evidence that short-range dynamic correlations start appearing above a magnetic field of about 5 T. Our demonstrations of the magnetic instability and the field-induced quantum phase transition are crucial for the quantum criticality, which may open a new route in experimental investigations of the quantum phase transition in heavy-fermion systems.
Field-induced magnetic instability and quantum criticality in the antiferromagnet CeCu2Ge2
Liu, Yi; Xie, Donghua; Wang, Xiaoying; Zhu, Kangwei; Yang, Ruilong
2016-01-01
The magnetic quantum criticality in strongly correlated electron systems has been considered to be closely related with the occurrence of unconventional superconductivity. Control parameters such as magnetic field, pressure or chemical doping are frequently used to externally tune the quantum phase transition for a deeper understanding. Here we report the research of a field-induced quantum phase transition using conventional bulk physical property measurements in the archetypal antiferromagnet CeCu2Ge2, which becomes superconductive under a pressure of about 10 GPa with Tc ~ 0.64 K. We offer strong evidence that short-range dynamic correlations start appearing above a magnetic field of about 5 T. Our demonstrations of the magnetic instability and the field-induced quantum phase transition are crucial for the quantum criticality, which may open a new route in experimental investigations of the quantum phase transition in heavy-fermion systems. PMID:26758347
Toward a dispersion model for magnetic reconnection: lessons from quantum vortex dynamics
NASA Astrophysics Data System (ADS)
Narita, Yasuhito
2015-04-01
The phenomenon of quantum vortex reconnection as realized by a turbulent helium superfluid offers astrophysical plasma physicists a great amount of hints and ideas to extract the essence of collisionless magnetic reconnection. Based on the recent review of quantum vortex reconnection [Narita, Y. and Baumjohann, W., Lessons on collisionless reconnection from quantum fluids, Front. Phys., 2, 76, 2014], a scenario of dispersion model for magnetic reconnection is proposed here. In this scenario, the dispersion effect causing the wave packet broadening plays a more essential role in reconnection than other effects such as anomalous resistivity, electron pressure anisotropy and stress, or electron inertia. The nonlinearity is neglected in the weak magnetic field region of reconnection (i.e., diffusion region), and the reconnection dynamics is given as a linear dispersive picture. The dispersion effect can be found not only in quantum mechanics (the Schroedinger equation) but also in plasma physics as dispersive waves (whistler waves, for example). While magnetic reconnection is often associated with turbulence, the dispersion model suggests that reconnection be a smooth transition of magnetic field line topology.
NASA Astrophysics Data System (ADS)
Wang, Jigang
2014-03-01
Research of non-equilibrium phase transitions of strongly correlated electrons is built around addressing an outstanding challenge: how to achieve ultrafast manipulation of competing magnetic/electronic phases and reveal thermodynamically hidden orders at highly non-thermal, femtosecond timescales? Recently we reveal a new paradigm called quantum femtosecond magnetism-photoinduced femtosecond magnetic phase transitions driven by quantum spin flip fluctuations correlated with laser-excited inter-atomic coherent bonding. We demonstrate an antiferromagnetic (AFM) to ferromagnetic (FM) switching during about 100 fs laser pulses in a colossal magneto-resistive manganese oxide. Our results show a huge photoinduced femtosecond spin generation, measured by magnetic circular dichroism, with photo-excitation threshold behavior absent in the picosecond dynamics. This reveals an initial quantum coherent regime of magnetism, while the optical polarization/coherence still interacts with the spins to initiate local FM correlations that compete with the surrounding AFM matrix. Our results thus provide a framework that explores quantum non-equilibrium kinetics to drive phase transitions between exotic ground states in strongly correlated elecrons, and raise fundamental questions regarding some accepted rules, such as free energy and adiabatic potential surface. This work is in collaboration with Tianqi Li, Aaron Patz, Leonidas Mouchliadis, Jiaqiang Yan, Thomas A. Lograsso, Ilias E. Perakis. This work was supported by the National Science Foundation (contract no. DMR-1055352). Material synthesis at the Ames Laboratory was supported by the US Department of Energy-Basic Energy Sciences (contract no. DE-AC02-7CH11358).
NASA Astrophysics Data System (ADS)
Dzebisashvili, D. M.; Khudaiberdyev, A. A.
2016-06-01
The specific features of quantum oscillations of the magnetization in quasi-two-dimensional wide-band-gap antiferromagnetic semimetals with a low concentration of charge carriers have been considered theoretically. It has been shown that, in these systems, the Fermi energy determined from the analysis of the frequency of the de Haas-van Alphen oscillations according to the standard procedure can differ significantly from the true value. For the correct determination of the Fermi energy in the canted phase, it has been proposed to analyze quantum oscillations of the magnetization M not as a function of the inverse magnetic field 1/ H, but as a function of 1/cosγ, where the angle γ characterizes the inclination angle of the magnetic field with respect to the plane of the quasi-two-dimensional semimetal.
Jahan K, Luhluh Boda, Aalu; Chatterjee, Ashok
2015-05-15
The problem of an exciton trapped in a three dimensional Gaussian quantum dot is studied in the presence of an external magnetic field. A variational method is employed to obtain the ground state energy of the exciton as a function of the quantum dot size, the confinement strength and the magnetic field. It is also shown that the variation of the size of the exciton with the radius of the quantum dot.
Single spins in diamond for quantum networks and magnetic sensing
NASA Astrophysics Data System (ADS)
Dutt, M. V. Gurudev
2010-06-01
Building scalable quantum information systems is a central challenge facing modern science. Single spins in diamond are a promising platform for distributed quantum information networks and precision measurements. I will discuss recent progress in this field demonstrating coherent operations with coupled electron-nuclear spin quantum registers and nanoscale precision magnetometry. Our experiments demonstrate addressing, preparation, and coherent control of individual nuclear spin qubits in the diamond lattice at room temperature. We have measured spin coherence times exceeding milliseconds, and observed coherent coupling to nearby electronic and nuclear spins. Robust initialization of a two-qubit register and transfer of arbitrary quantum states between electron and nuclear spin qubits has been achieved. Our results show that coherent operations are possible with individual solid-state qubits whose coherence properties approach those for isolated atoms and ions. The resulting electron-nuclear few-qubit registers can potentially serve as small processor nodes in a quantum network where the electron spins are coupled by optical photons.
NASA Astrophysics Data System (ADS)
Zhu, Zhenni; Wu, Zhengwei; Li, Chunhua; Yang, Weihong
2014-11-01
A model for the nonlinear properties of obliquely propagating electron acoustic solitary waves in a two-electron populated relativistically quantum magnetized plasma is presented. By using the standard reductive perturbation technique, the Zakharov-Kuznetsov (ZK) equation is derived and this equation gives the solitary wave solution. It is observed that the relativistic effects, the ratio of the cold to hot electron unperturbed number density and the magnetic field normalized by electron cyclotron frequency significantly influence the solitary structures.
Intrinsic high magnetism in SnO{sub 2} quantum dots
Venkataramana, Bonu Das, A. Dhara, S.; Tyagi, A. K.; Sardar, Manas
2014-04-24
High magnetic moment was observed in SnO{sub 2} quantum dots (QDs) which were prepared by a soft chemical method. SnO{sub 2} QDs were characterized for morphological, structural and optical properties using high resolution tunneling electron microscopy and photoluminescence (PL) spectroscopy, respectively. Magnetism occurred in QDs SnO{sub 2} due to dominant oxygen defects, were studied using PL measurements.
Individual Mammalian Cell Magnetic Measurements with a Superconducting Quantum Interference Device
NASA Astrophysics Data System (ADS)
Palmstrom, Johanna C.; Brewer, Kimberly; Tee, Sui Seng; Theis, Eric; Rutt, Brian; Moler, Kathryn A.
2015-03-01
Magnetism can be introduced into otherwise nonmagnetic cells by the uptake of superparamagnetic iron oxide (SPIO) nanoparticles. SPIO nanoparticles are used in numerous biomedical applications including cellular therapies and targeted drug delivery. Currently there are few tools capable of characterizing individual magnetic nanoparticles and the magnetic properties of individual mammalian cells loaded with SPIO. Our scanning superconducting quantum interference devices (SQUIDs) are good candidates for these measurements due to their high sensitivity to magnetic dipole moments (approx. 200 μb/ √Hz) In this study, we use a scanning SQUID to image the magnetic flux from SPIO loaded H1299 lung cancer cells. We find that the magnetic moment spatially varies inside the cell with each cell having a unique distribution of moments. We also correlate these magnetic images with optical and scanning electron microscope images. These results show that the SQUID is a useful tool for imaging biological magnetism. The visualization of single cell magnetism and the quantification of magnetic dipole moments in magnetically labeled cells can be used to optimize conventional biological magnetic imaging techniques, such as MRI.
Quantum rings of non-uniform thickness in magnetic field
Rodríguez-Prada, F. A.; García, L. F.; Mikhailov, I. D.
2014-05-15
We consider a model of crater-shaped quantum dot in form of a thin layer whose thickness linearly increases with the distance from the axis. We show that one-particle wave equation for the electron confined in such structure can be completely separated in the adiabatic limit when the quantum dot thickness is much smaller than its lateral dimension. Analytical solutions found for this model has been used as base functions for analysing the effect of non-homogeneity on the electronic spectrum in the framework of the exact diagonalization method.
Quantum oscillations of magnetization in tight-binding electrons on a honeycomb lattice
NASA Astrophysics Data System (ADS)
Kishigi, Keita; Hasegawa, Yasumasa
2014-08-01
We show that quantum oscillations of the magnetization can occur when the Fermi surface consists of points (massless Dirac points) or even when the chemical potential is in an energy gap by studying tight-binding electrons on a honeycomb lattice in a uniform magnetic field. The quantum oscillations of the magnetization as a function of the inverse magnetic field are known as de Haas-van Alphen (dHvA) oscillations and the frequency is proportional to the area of the Fermi surface. The dominant period of the oscillations shown in this paper corresponds to the area of the first Brillouin zone and its phase is zero. The origin of these quantum oscillations is the characteristic magnetic field dependence of the energy known as the Hofstadter butterfly and the Harper broadening of Landau levels. These oscillations are not caused by the crossing of the chemical potential and Landau levels, which is the case in dHvA oscillations. These oscillations can be observed experimentally in systems with a large supercell such as a graphene antidot lattice or ultracold atoms in an optical lattice at an external magnetic field of a few Tesla when the area of the supercell is 104 times larger than that of graphene.
Modulation of a compressional electromagnetic wave in a magnetized electron-positron quantum plasma.
Amin, M R
2015-09-01
Amplitude modulation of a compressional electromagnetic wave in a strongly magnetized electron-positron pair plasma is considered in the quantum magnetohydrodynamic regime. The important ingredients of this study are the inclusion of the external strong magnetic field, Fermi quantum degeneracy pressure, particle exchange potential, quantum diffraction effects via the Bohm potential, and dissipative effect due to collision of the charged carriers. A modified-nonlinear Schödinger equation is developed for the compressional magnetic field of the electromagnetic wave by employing the standard reductive perturbation technique. The linear and nonlinear dispersions of the electromagnetic wave are discussed in detail. For some parameter ranges, relevant to dense astrophysical objects such as the outer layers of white dwarfs, neutron stars, and magnetars, etc., it is found that the compressional electromagnetic wave is modulationally unstable and propagates as a dissipated electromagnetic wave. It is also found that the quantum effects due to the particle exchange potential and the Bohm potential are negligibly small in comparison to the effects of the Fermi quantum degeneracy pressure. The numerical results on the growth rate of the modulation instability is also presented.
Manifestation of magnetic quantum fluctuations in the dielectric properties of a multiferroic
NASA Astrophysics Data System (ADS)
Kim, Jae Wook; Khim, Seunghyun; Chun, Sae Hwan; Jo, Y.; Balicas, L.; Yi, H. T.; Cheong, S.-W.; Harrison, N.; Batista, C. D.; Hoon Han, Jung; Hoon Kim, Kee
2014-07-01
Insulating magnets can display novel signatures of quantum fluctuations as similar to the case of metallic magnets. However, their weak spin-lattice coupling has made such observations challenging. Here we find that antiferromagnetic (AF) quantum fluctuations manifest in the dielectric properties of multiferroic Ba2CoGe2O7, where a ferroelectric polarization develops concomitant to an AF ordering. Upon application of a magnetic field (H), dielectric constant shows a characteristic power-law dependence near absolute zero temperature and close to the critical field Hc=37.1 T due to enhanced AF quantum fluctuations. When H>Hc, the dielectric constant shows the temperature-dependent anomalies that reflect a crossover from a field-tuned quantum critical to a gapped spin-polarized state. We uncover theoretically that a linear relation between AF susceptibility and dielectric constant stems from the generic magnetoelectric coupling and directly explains the experimental findings, opening a new pathway for studying quantum criticality in condensed matter.
NASA Astrophysics Data System (ADS)
Val'kov, V. V.; Aksenov, S. V.; Ulanov, E. A.
2015-02-01
We present a solution for the problem of quantum electron transport through a magnetic atom adsorbed inside a break junction with paramagnetic metal electrodes. In agreement with experimental data, it was assumed that the conduction electrons experience inelastic scattering by the adsorbate due to s-d(f)-exchange interaction. The Keldysh technique was employed to obtain a general expression describing a current through the multilevel structure at finite temperatures in terms of the nonequilibrium Green's function. The use of the atomic representation allowed to exactly account for the non-equidistant structure of the energy spectrum of a magnetic atom and to simplify substantially the application of the Wick theorem for construction of the nonequilibrium diagrammatic technique for the Hubbard operators. The calculation of the current-voltage characteristics of the magnetic adatom in the tunnel regime at low temperatures revealed the presence of regions with a negative differential conductance in a magnetic field.
Time-resolved magnetophotoluminescence studies of magnetic polaron dynamics in type-II quantum dots
NASA Astrophysics Data System (ADS)
Barman, B.; Oszwałdowski, R.; Schweidenback, L.; Russ, A. H.; Pientka, J. M.; Tsai, Y.; Chou, W.-C.; Fan, W. C.; Murphy, J. R.; Cartwright, A. N.; Sellers, I. R.; Petukhov, A. G.; Žutić, I.; McCombe, B. D.; Petrou, A.
2015-07-01
We used continuous wave photoluminescence (cw-PL) and time-resolved photoluminescence (TR-PL) spectroscopy to compare the properties of magnetic polarons (MP) in two related spatially indirect II-VI epitaxially grown quantum dot systems. In the ZnTe /(Zn ,Mn )Se system the holes are confined in the nonmagnetic ZnTe quantum dots (QDs), and the electrons reside in the magnetic (Zn,Mn)Se matrix. On the other hand, in the (Zn ,Mn )Te /ZnSe system, the holes are confined in the magnetic (Zn,Mn)Te QDs, while the electrons remain in the surrounding nonmagnetic ZnSe matrix. The magnetic polaron formation energies EMP in both systems were measured from the temporal redshift of the band-edge emission. The magnetic polaron exhibits distinct characteristics depending on the location of the Mn ions. In the ZnTe /(Zn ,Mn )Se system the magnetic polaron shows conventional behavior with EMP decreasing with increasing temperature T and increasing magnetic field B . In contrast, EMP in the (Zn ,Mn )Te /ZnSe system has unconventional dependence on temperature T and magnetic field B ; EMP is weakly dependent on T as well as on B . We discuss a possible origin for such a striking difference in the MP properties in two closely related QD systems.
Will spin-relaxation times in molecular magnets permit quantum information processing?
NASA Astrophysics Data System (ADS)
Ardavan, Arzhang
2007-03-01
Certain computational tasks can be efficiently implemented using quantum logic, in which the information-carrying elements are permitted to exist in quantum superpositions. To achieve this in practice, a physical system that is suitable for embodying quantum bits (qubits) must be identified. Some proposed scenarios employ electron spins in the solid state, for example phosphorous donors in silicon, quantum dots, heterostructures and endohedral fullerenes, motivated by the long electron-spin relaxation times exhibited by these systems. An alternative electron-spin based proposal exploits the large number of quantum states and the non-degenerate transitions available in high spin molecular magnets. Although these advantages have stimulated vigorous research in molecular magnets, the key question of whether the intrinsic spin relaxation times are long enough has hitherto remained unaddressed. Using X-band pulsed electron spin resonance, we measure the intrinsic spin-lattice (T1) and phase coherence (T2) relaxation times in molecular nanomagnets for the first time. In Cr7M heterometallic wheels, with M = Ni and Mn, phase coherence relaxation is dominated by the coupling of the electron spin to protons within the molecule. In deuterated samples T2 reaches 3 μs at low temperatures, which is several orders of magnitude longer than the duration of spin manipulations, satisfying a prerequisite for the deployment of molecular nanomagnets in quantum information applications.
NASA Astrophysics Data System (ADS)
Ghosh, Sayandip; Raghuvanshi, Nimisha; Mohapatra, Shubhajyoti; Kumar, Ashish; Singh, Avinash
2016-09-01
Effective spin couplings and spin fluctuation induced quantum corrections to sublattice magnetization are obtained in the (π,0) AF state of a realistic three-orbital interacting electron model involving xz, yz and xy Fe 3d orbitals, providing insight into the multi-orbital quantum antiferromagnetism in iron pnictides. The xy orbital is found to be mainly responsible for the generation of strong ferromagnetic spin coupling in the b direction, which is critically important to fully account for the spin wave dispersion as measured in inelastic neutron scattering experiments. The ferromagnetic spin coupling is strongly suppressed as the xy band approaches half filling, and is ascribed to particle-hole exchange in the partially filled xy band. The strongest AF spin coupling in the a direction is found to be in the orbital off-diagonal sector involving the xz and xy orbitals. First order quantum corrections to sublattice magnetization are evaluated for the three orbitals, and yield a significant 37% average reduction from the Hartree-Fock value.
NASA Astrophysics Data System (ADS)
Ghosh, Sayandip; Raghuvanshi, Nimisha; Mohapatra, Shubhajyoti; Kumar, Ashish; Singh, Avinash
2016-09-01
Effective spin couplings and spin fluctuation induced quantum corrections to sublattice magnetization are obtained in the (π,0) AF state of a realistic three-orbital interacting electron model involving xz, yz and xy Fe 3d orbitals, providing insight into the multi-orbital quantum antiferromagnetism in iron pnictides. The xy orbital is found to be mainly responsible for the generation of strong ferromagnetic spin coupling in the b direction, which is critically important to fully account for the spin wave dispersion as measured in inelastic neutron scattering experiments. The ferromagnetic spin coupling is strongly suppressed as the xy band approaches half filling, and is ascribed to particle-hole exchange in the partially filled xy band. The strongest AF spin coupling in the a direction is found to be in the orbital off-diagonal sector involving the xz and xy orbitals. First order quantum corrections to sublattice magnetization are evaluated for the three orbitals, and yield a significant 37% average reduction from the Hartree–Fock value.
Bose-Einstein Condensation and Bose Glasses in an S = 1 Organo-metallic quantum magnet
Zapf, Vivien
2012-06-01
I will speak about Bose-Einstein condensation (BEC) in quantum magnets, in particular the compound NiCl2-4SC(NH2)2. Here a magnetic field-induced quantum phase transition to XY antiferromagnetism can be mapped onto BEC of the spins. The tuning parameter for BEC transition is the magnetic field rather than the temperature. Some interesting phenomena arise, for example the fact that the mass of the bosons that condense can be strongly renormalized by quantum fluctuations. I will discuss the utility of this mapping for both understanding the nature of the quantum magnetism and testing the thermodynamic limit of Bose-Einstein Condensation. Furthermore we can dope the system in a clean and controlled way to create the long sought-after Bose Glass transition, which is the bosonic analogy of Anderson localization. I will present experiments and simulations showing evidence for a new scaling exponent, which finally makes contact between theory and experiments. Thus we take a small step towards the difficult problem of understanding the effect of disorder on bosonic wave functions.
Propagation of surface waves on a semi-bounded quantum magnetized collisional plasma
Niknam, A. R.; Taheri Boroujeni, S.; Khorashadizadeh, S. M.
2013-12-15
The propagation of surface waves on a semi-bounded quantum plasma in the presence of the external magnetic field and collisional effects is investigated by using quantum magnetohydrodynamics model. A general analytical expression for the dispersion relation of surface waves is obtained by considering the boundary conditions. It is shown that, in some special cases, the obtained dispersion relation reduces to the results reported in previous works. It is also indicated that the quantum, external magnetic field and collisional effects can facilitate the propagation of surface waves on a semi-bounded plasma. In addition, it is found that the growth rate of the surface wave instability is enhanced by increasing the collision frequency and plasmonic parameter.
Inverse parabolic quantum dot: The transition energy under magnetic field effect
NASA Astrophysics Data System (ADS)
Safwan, S. A.; El Meshed, Nagwa
2016-08-01
We present here, the evolution of the transition energy with a static magnetic field, when the electron and the hole are confined in inverse parabolic quantum dot (IPQD). The unexpected behavior is found, at the weak confinement regime the conduction band minimum and the top of valance band change from s-state to p-state or d-state for confined electron and hole inside IPQD, respectively. The strength of the inverse parabolic potential (potential hump) inside a quantum dot has the upper hand in tuning the ground state momentum for both electron and hole, and consequently their interband transition energy is changed. Knowing that this is not the case for the other types of potentials. The quantum size, the magnetic field and inverse potential hump effects on electron and hole ground and excited states are discussed.
NASA Astrophysics Data System (ADS)
Ohanyan, Vadim; Rojas, Onofre; Strečka, Jozef; Bellucci, Stefano
2015-12-01
We examine the general features of the noncommutativity of the magnetization operator and Hamiltonian for small quantum spin clusters. The source of this noncommutativity can be a difference in the Landé g factors for different spins in the cluster, X Y anisotropy in the exchange interaction, and the presence of the Dzyaloshinskii-Moriya term in a direction different from the direction of the magnetic field. As a result, zero-temperature magnetization curves for small spin clusters mimic those for the macroscopic systems with the band(s) of magnetic excitations, i.e., for the given eigenstate of the spin cluster the corresponding magnetic moment can be an explicit function of the external magnetic field yielding the nonconstant (nonplateau) form of the magnetization curve within the given eigenstate. In addition, the X Y anisotropy makes the saturated magnetization (the eigenstate when all spins in cluster are aligned along the magnetic field) inaccessible for finite magnetic field magnitude (asymptotical saturation). We demonstrate all these features on three examples: a spin-1/2 dimer, mixed spin-(1/2,1) dimer, and a spin-1/2 ring trimer. We consider also the simplest Ising-Heisenberg chain, the Ising-X Y Z diamond chain, with four different g factors. In the chain model the magnetization curve has a more complicated and nontrivial structure than that for clusters.
Giant quantum oscillations of magnetic Landau damping in aluminum
NASA Astrophysics Data System (ADS)
Skobov, V. G.; Chernov, A. S.
2015-07-01
The effect of quantization of the electron energy in a magnetic field on the collisionless damping of radio-frequency modes in aluminum has been investigated theoretically. In the geometry where a propagation vector k and a constant magnetic field H are directed along the C 4 axis in aluminum there is a magnetic Landau damping caused by electrons whose orbits are inclined to the transverse plane. Despite a relatively low concentration of electrons, this damping can significantly affect the damping of a helicon and a doppleron. It has been shown that the quantization of the electron energy leads to giant oscillations of the damping of these modes.
Quantum theory of the dielectric constant of a magnetized plasma and astrophysical applications. I.
NASA Technical Reports Server (NTRS)
Canuto, V.; Ventura, J.
1972-01-01
A quantum mechanical treatment of an electron plasma in a constant and homogeneous magnetic field is considered, with the aim of (1) defining the range of validity of the magnetoionic theory (2) studying the deviations from this theory, in applications involving high densities, and intense magnetic field. While treating the magnetic field exactly, a perturbation approach in the photon field is used to derive general expressions for the dielectric tensor. Numerical estimates on the range of applicability of the magnetoionic theory are given for the case of the 'one-dimensional' electron gas, where only the lowest Landau level is occupied.
Degree of circular polarization in II-VI diluted magnetic semiconductor quantum dots
NASA Astrophysics Data System (ADS)
Rana, Shivani; Sen, Pratima; Sen, Pranay Kumar
2012-07-01
Degree of circular polarization (DCP) in II-VI diluted magnetic semiconductor quantum dots (QDs) has been studied analytically. Energy levels have been calculated using Luttinger-Kohn Hamiltonian and effective mass approximation. Effects due to application of externa magnetic field have been investigated, followed by calculation of transition dipole moment and DCP. Numerical estimates made for Mn-doped CdSe/ZnSe QDs show that DCP in undoped QDs is negligible while transition metal ion doping yields substantial polarization rotation (≈-2.20%) even at moderate magnetic fields (≈0.5T).
Quantum correlations of magnetic impurities by a multiple electron scattering in carbon nanotubes
NASA Astrophysics Data System (ADS)
Gamboa Angulo, Didier; Cordourier Maruri, Guillermo; de Coss Gómez, Romeo
In this work we analyze the quantum correlations and polarizations states of magnetic impurities spins, when a multiple electron scattering was taken place. A sequence of non-correlated electrons interacts through scattering producing quantum correlation which will have an impact on the electronic transmission. We consider a short range Heisenberg interaction between ballistic electron and static impurities. We analyze the cases when the electron scattering is produce by one and two impurities, obtaining the electronic transmission rates. Concurrence and fidelity calculations are performed to obtain the level of quantum entanglement and polarization correlations. We also discuss the possible application of this model to metallic and semiconductor carbon nanotubes, which could have important implications on spintronics and quantum information devices.
Fritsch, Katharina; Ehlers, G.; Rule, K. C.; Habicht, Klaus; Ramazanoglu, Mehmet K.; Dabkowska, H. A.; Gaulin, Bruce D.
2015-11-05
We study the application of a magnetic field transverse to the easy axis, Ising direction in the quasi-two-dimensional kagome staircase magnet, Co3V2O8, induces three quantum phase transitions at low temperatures, ultimately producing a novel high field polarized state, with two distinct sublattices. New time-of-flight neutron scattering techniques, accompanied by large angular access, high magnetic field infrastructure allow the mapping of a sequence of ferromagnetic and incommensurate phases and their accompanying spin excitations. Also, at least one of the transitions to incommensurate phases at μ0Hc1~6.25 T and μ0Hc2~7 T is discontinuous, while the final quantum critical point at μ0Hc3~13 T ismore » continuous.« less
NASA Astrophysics Data System (ADS)
Fritsch, K.; Ehlers, G.; Rule, K. C.; Habicht, K.; Ramazanoglu, M.; Dabkowska, H. A.; Gaulin, B. D.
2015-11-01
The application of a magnetic field transverse to the easy axis, Ising direction in the quasi-two-dimensional kagome staircase magnet, Co3V2O8 , induces three quantum phase transitions at low temperatures, ultimately producing a novel high field polarized state, with two distinct sublattices. New time-of-flight neutron scattering techniques, accompanied by large angular access, high magnetic field infrastructure allow the mapping of a sequence of ferromagnetic and incommensurate phases and their accompanying spin excitations. At least one of the transitions to incommensurate phases at μ0Hc 1˜6.25 T and μ0Hc 2˜7 T is discontinuous, while the final quantum critical point at μ0Hc 3˜13 T is continuous.
Nuclear magnetic resonance detection and spectroscopy of single proteins using quantum logic
NASA Astrophysics Data System (ADS)
Lovchinsky, I.; Sushkov, A. O.; Urbach, E.; de Leon, N. P.; Choi, S.; De Greve, K.; Evans, R.; Gertner, R.; Bersin, E.; Müller, C.; McGuinness, L.; Jelezko, F.; Walsworth, R. L.; Park, H.; Lukin, M. D.
2016-02-01
Nuclear magnetic resonance spectroscopy is a powerful tool for the structural analysis of organic compounds and biomolecules but typically requires macroscopic sample quantities. We use a sensor, which consists of two quantum bits corresponding to an electronic spin and an ancillary nuclear spin, to demonstrate room temperature magnetic resonance detection and spectroscopy of multiple nuclear species within individual ubiquitin proteins attached to the diamond surface. Using quantum logic to improve readout fidelity and a surface-treatment technique to extend the spin coherence time of shallow nitrogen-vacancy centers, we demonstrate magnetic field sensitivity sufficient to detect individual proton spins within 1 second of integration. This gain in sensitivity enables high-confidence detection of individual proteins and allows us to observe spectral features that reveal information about their chemical composition.
Quantum melting of magnetic order in an organic dimer Mott-insulating system
NASA Astrophysics Data System (ADS)
Naka, Makoto; Ishihara, Sumio
2016-05-01
Quantum entanglement effects between the electronic spin and charge degrees of freedom are examined in an organic molecular solid, termed a dimer Mott-insulating system, in which molecular dimers are arranged in a crystal as fundamental units. A low energy effective model includes an antisymmetric exchange interaction, as one of the dominant magnetic interactions. This interaction favors a 90 deg spin configuration, and competes with the Heisenberg-type exchange interaction. Stabilities of the magnetic ordered phases are examined by using the spin-wave theory, as well as the Schwinger-boson theory. It is found that the spin-charge interaction promotes an instability of the long-range magnetic ordered state around a parameter region where two spin-spiral phases are merged. Implication for the quantum spin liquid state observed in κ -(BEDT-TTF)2Cu2 (CN) 3 is discussed.
Nuclear magnetic resonance detection and spectroscopy of single proteins using quantum logic.
Lovchinsky, I; Sushkov, A O; Urbach, E; de Leon, N P; Choi, S; De Greve, K; Evans, R; Gertner, R; Bersin, E; Müller, C; McGuinness, L; Jelezko, F; Walsworth, R L; Park, H; Lukin, M D
2016-02-19
Nuclear magnetic resonance spectroscopy is a powerful tool for the structural analysis of organic compounds and biomolecules but typically requires macroscopic sample quantities. We use a sensor, which consists of two quantum bits corresponding to an electronic spin and an ancillary nuclear spin, to demonstrate room temperature magnetic resonance detection and spectroscopy of multiple nuclear species within individual ubiquitin proteins attached to the diamond surface. Using quantum logic to improve readout fidelity and a surface-treatment technique to extend the spin coherence time of shallow nitrogen-vacancy centers, we demonstrate magnetic field sensitivity sufficient to detect individual proton spins within 1 second of integration. This gain in sensitivity enables high-confidence detection of individual proteins and allows us to observe spectral features that reveal information about their chemical composition.
Magnetic Torque Anomaly in the Quantum Limit of Weyl and Dirac Semimetals
NASA Astrophysics Data System (ADS)
Nair, Nityan L.; Moll, Philip J. W.; Potter, Andrew C.; Ramshaw, Brad; Modic, Kimberly; Riggs, Scott; Zeng, Bin; Ghimire, Nirmal; Bauer, Eric; Kealhofer, Robert; Li, Zhenglu; Louie, Steven; Ronning, Filip; Analytis, James G.
Three dimensional Dirac and Weyl semimetals, characterized by bulk quasiparticles that behave as massless, linearly dispersing Dirac or Weyl fermions, have excited physicists with their unique topological properties and potential for applications. The experimental signatures of Weyl or Dirac fermions, however, are often subtle and indirect, especially in systems where they coexist with trivial electrons. Here, we report a novel method by which these topological systems can be unambiguously experimentally identified. Magnetic torque measurements were performed on the Weyl semimetal NbAs in high magnetic field, showing a large anomaly upon entering the quantum limit. The torque exhibits a striking sign reversal, corresponding to a change in the magnetic anisotropy that is a direct result of the topological properties of the charge carriers. This result can be generalized to other Dirac and Weyl semimetal systems and establishes quantum limit torque measurements as a simple and direct experimental method of distinguishing topologically non-trivial Weyl and Dirac systems from trivial semiconductors.
Nuclear magnetic resonance detection and spectroscopy of single proteins using quantum logic.
Lovchinsky, I; Sushkov, A O; Urbach, E; de Leon, N P; Choi, S; De Greve, K; Evans, R; Gertner, R; Bersin, E; Müller, C; McGuinness, L; Jelezko, F; Walsworth, R L; Park, H; Lukin, M D
2016-02-19
Nuclear magnetic resonance spectroscopy is a powerful tool for the structural analysis of organic compounds and biomolecules but typically requires macroscopic sample quantities. We use a sensor, which consists of two quantum bits corresponding to an electronic spin and an ancillary nuclear spin, to demonstrate room temperature magnetic resonance detection and spectroscopy of multiple nuclear species within individual ubiquitin proteins attached to the diamond surface. Using quantum logic to improve readout fidelity and a surface-treatment technique to extend the spin coherence time of shallow nitrogen-vacancy centers, we demonstrate magnetic field sensitivity sufficient to detect individual proton spins within 1 second of integration. This gain in sensitivity enables high-confidence detection of individual proteins and allows us to observe spectral features that reveal information about their chemical composition. PMID:26847544
NASA Astrophysics Data System (ADS)
Wang, Yuan; Zhang, Yanchao; Huang, Chuankun; Chen, Jincan
2015-11-01
A general model of a single orbital interacting quantum dot embed into two metal leads is established, in which an external applied magnetic field is considered and a linear fade of the Coulomb energy resulting from the energy level splitting is introduced. The occupation probabilities of quantum states are determined by the master equation under the steady state condition. The expressions of matter fluxes, heat fluxes, power output, and efficiency are derived. The effects of both the magnetic field and energy level on the performance are discussed. The maximum power output and efficiency are calculated. The optimal regions of the energy level and magnetic field are determined. Some important conclusions in literature can be directly deduced under the different extreme conditions of the present model.
A type of novel fluorescent magnetic carbon quantum dots for cells imaging and detection.
Su, Xi; Xu, Yi; Che, Yulan; Liao, Xin; Jiang, Yan
2015-12-01
A new type of multifunctional fluorescent magnetic carbon quantum dots SPIO@CQDs(n) ([superparamagnetic iron oxide nanoparticles (SPIO), carbon quantum dots, (CQDs)]) with magnetic and fluorescence properties was designed and prepared through layer-by-layer self-assembly method. The as-synthesized SPIO@CQDs(n) exhibited different emission colors including blue, green, and red when they were excited at different excitation wavelengths, and its fluorescent intensity increased as the increase of CQD layer (n). SPIO@CQDs(n) with quite low toxicity could mark cytoplasm with fluorescence by means of nonimmune markers. The mixture sample of liver cells L02 and hepatoma carcinoma cells HepG2 was taken as an example, and HepG2 cells were successfully separated and detected effectively by SPIO@CQDs(n), with a separation rate of 90.31%. Importantly, the designed and prepared SPIO@CQDs( n ) are certified to be wonderful biological imaging and magnetic separation regents.
Magnetic bead-quantum dot assay for detection of a biomarker for traumatic brain injury
NASA Astrophysics Data System (ADS)
Kim, Chloe; Searson, Peter C.
2015-10-01
Current diagnostic methods for traumatic brain injury (TBI), which accounts for 15% of all emergency room visits, are limited to neuroimaging modalities. The challenges of accurate diagnosis and monitoring of TBI have created the need for a simple and sensitive blood test to detect brain-specific biomarkers. Here we report on an assay for detection of S100B, a putative biomarker for TBI, using antibody-conjugated magnetic beads for capture of the protein, and antibody-conjugated quantum dots for optical detection. From Western Blot, we show efficient antigen capture and concentration by the magnetic beads. Using magnetic bead capture and quantum dot detection in serum samples, we show a wide detection range and detection limit below the clinical cut-off level.Current diagnostic methods for traumatic brain injury (TBI), which accounts for 15% of all emergency room visits, are limited to neuroimaging modalities. The challenges of accurate diagnosis and monitoring of TBI have created the need for a simple and sensitive blood test to detect brain-specific biomarkers. Here we report on an assay for detection of S100B, a putative biomarker for TBI, using antibody-conjugated magnetic beads for capture of the protein, and antibody-conjugated quantum dots for optical detection. From Western Blot, we show efficient antigen capture and concentration by the magnetic beads. Using magnetic bead capture and quantum dot detection in serum samples, we show a wide detection range and detection limit below the clinical cut-off level. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05608j
NASA Astrophysics Data System (ADS)
Pelliccione, Matthew; Jenkins, Alec; Ovartchaiyapong, Preeti; Reetz, Christopher; Emmanuelidu, Eve; Ni, Ni; Bleszynski Jayich, Ania
The nitrogen vacancy (NV) defect in diamond has emerged as a promising candidate for high resolution magnetic imaging based on its atomic size and quantum-limited sensing capabilities afforded by long spin coherence times. Although the NV center has been successfully implemented as a nanoscale scanning magnetic probe at room temperature, it has remained an outstanding challenge to extend this capability to cryogenic temperatures, where many solid-state systems exhibit non-trivial magnetic order. In this talk, we present NV magnetic imaging at T = 6 K, first benchmarking the technique with a magnetic hard disk sample, then utilizing the technique to image vortices in the iron pnictide superconductor BaFe2(As0.7P0.3)2 with Tc = 30 K. In addition, we discuss other candidate solid-state systems that can benefit from the high spatial resolution and field sensitivity of the scanning NV magnetometer.
Exciton effective mass enhancement in coupled quantum wells in electric and magnetic fields
NASA Astrophysics Data System (ADS)
Wilkes, J.; Muljarov, E. A.
2016-02-01
We present a calculation of exciton states in semiconductor coupled quantum wells in the presence of electric and magnetic fields applied perpendicular to the QW plane. The exciton Schrödinger equation is solved in real space in three-dimensions to obtain the Landau levels of both direct and indirect excitons. Calculation of the exciton energy levels and oscillator strengths enables mapping of the electric and magnetic field dependence of the exciton absorption spectrum. For the ground state of the system, we evaluate the Bohr radius, optical lifetime, binding energy and dipole moment. The exciton mass renormalization due to the magnetic field is calculated using a perturbative approach. We predict a non-monotonous dependence of the exciton ground state effective mass on magnetic field. Such a trend is explained in a classical picture, in terms of the ground state tending from an indirect to a direct exciton with increasing magnetic field.
The quantum equations of state of plasma under the influence of a weak magnetic field
Hussein, N. A.; Eisa, D. A.; Eldin, M. G.
2012-05-15
The aim of this paper is to calculate the magnetic quantum equations of state of plasma, the calculation is based on the magnetic binary Slater sum in the case of low density. We consider only the thermal equilibrium plasma in the case of n{lambda}{sub ab}{sup 3} Much-Less-Than 1, where {lambda}{sub ab}{sup 2}=( Planck-Constant-Over-Two-Pi {sup 2}/m{sub ab}KT) is the thermal De Broglie wave length between two particles. The formulas contain the contributions of the magnetic field effects. Using these results we compute the magnetization and the magnetic susceptibility. Our equation of state is compared with others.
NASA Astrophysics Data System (ADS)
Kalmykov, Yuri P.; Titov, Serguey V.; Coffey, William T.
2015-11-01
The nonlinear ac stationary response of uniaxial paramagnets and superparamagnets—nanoscale solids or clusters with spin number S ˜100-104 —in superimposed uniform ac and dc bias magnetic fields of arbitrary strength, each applied along the easy axis of magnetization, is determined by solving the evolution equation for the reduced density matrix represented as a finite set of three-term differential-recurrence relations for its diagonal matrix elements. The various harmonic components arising from the nonlinear response of the magnetization, dynamic magnetic hysteresis loops, etc., are then evaluated via matrix continued fractions indicating a pronounced dependence of the response on S arising from the quantum spin dynamics, which differ markedly from the magnetization dynamics of classical nanomagnets. In the linear response approximation, the results concur with existing solutions.
Magnetic moments of light nuclei from lattice quantum chromodynamics
Beane, S. R.; Chang, E.; Cohen, S.; Detmold, W.; Lin, H. W.; Orginos, K.; Parreño, A.; Savage, M. J.; Tiburzi, B. C.
2014-12-16
We present the results of lattice QCD calculations of the magnetic moments of the lightest nuclei, the deuteron, the triton and 3He, along with those of the neutron and proton. These calculations, performed at quark masses corresponding to mπ ~ 800 MeV, reveal that the structure of these nuclei at unphysically heavy quark masses closely resembles that at the physical quark masses. We find that the magnetic moment of 3He differs only slightly from that of a free neutron, as is the case in nature, indicating that the shell-model configuration of two spin-paired protons and a valence neutron captures itsmore » dominant structure. Similarly a shell-model-like moment is found for the triton, μ3H ~ μp. The deuteron magnetic moment is found to be equal to the nucleon isoscalar moment within the uncertainties of the calculations.« less
Measurement of radiation-pressure-induced optomechanical dynamics in a suspended Fabry-Perot cavity
Corbitt, Thomas; Ottaway, David; Innerhofer, Edith; Pelc, Jason; Mavalvala, Nergis
2006-08-15
We report on experimental observation of radiation-pressure induced effects in a high-power optical cavity. These effects play an important role in next-generation gravitational wave detectors, as well as in quantum nondemolition interferometers. We measure the properties of an optical spring, created by coupling of an intense laser field to the pendulum mode of a suspended mirror, and also the parametric instability (PI) that arises from the coupling between acoustic modes of the cavity mirrors and the cavity optical mode. We measure an unprecedented optical rigidity of K=(3.08{+-}0.09)x10{sup 4} N/m, corresponding to an optical rigidity that is 6000 times stiffer than the mechanical stiffness, and PI strength R{approx_equal}3. We measure the unstable nature of the optical spring resonance, and demonstrate that the PI can be stabilized by feedback to the frequency of the laser source.
Properties of strong-coupling magneto-bipolaron qubit in quantum dot under magnetic field
NASA Astrophysics Data System (ADS)
Xu-Fang, Bai; Ying, Zhang; Wuyunqimuge; Eerdunchaolu
2016-07-01
Based on the variational method of Pekar type, we study the energies and the wave-functions of the ground and the first-excited states of magneto-bipolaron, which is strongly coupled to the LO phonon in a parabolic potential quantum dot under an applied magnetic field, thus built up a quantum dot magneto-bipolaron qubit. The results show that the oscillation period of the probability density of the two electrons in the qubit decreases with increasing electron–phonon coupling strength α, resonant frequency of the magnetic field ω c, confinement strength of the quantum dot ω 0, and dielectric constant ratio of the medium η the probability density of the two electrons in the qubit oscillates periodically with increasing time t, angular coordinate φ 2, and dielectric constant ratio of the medium η the probability of electron appearing near the center of the quantum dot is larger, and the probability of electron appearing away from the center of the quantum dot is much smaller. Project supported by the Natural Science Foundation of Hebei Province, China (Grant No. E2013407119) and the Items of Institution of Higher Education Scientific Research of Hebei Province and Inner Mongolia, China (Grant Nos. ZD20131008, Z2015149, Z2015219, and NJZY14189).
Pumera, Martin; Castañeda, Maria Teresa; Pividori, Maria Isabel; Eritja, Ramon; Merkoçi, Arben; Alegret, Salvador
2005-10-11
A novel gold nanoparticle-based protocol for detection of DNA hybridization based on a magnetically trigged direct electrochemical detection of gold quantum dot tracers is described. It relies on binding target DNA (here called DNA1) with Au(67) quantum dot in a ratio 1:1, followed by a genomagnetic hybridization assay between Au(67)-DNA1 and complementary probe DNA (here called DNA2) marked paramagnetic beads. Differential pulse voltammetry is used for a direct voltammetric detection of resulting Au(67) quantum dot-DNA1/DNA2-paramagnetic bead conjugate on magnetic graphite-epoxy composite electrode. The characterization, optimization, and advantages of the direct electrochemical detection assay for target DNA are demonstrated. The two main highlights of presented assay are (1) the direct voltammetric detection of metal quantum dots obviates their chemical dissolution and (2) the Au(67) quantum dot-DNA1/DNA2-paramagnetic bead conjugate does not create the interconnected three-dimensional network of Au-DNA duplex-paramagnetic beads as previously developed nanoparticle DNA assays, pushing down the achievable detection limits.
Numerical and theoretical study of Bernstein modes in a magnetized quantum plasma
NASA Astrophysics Data System (ADS)
Eliasson, Bengt; Shukla, Padma K.
2008-10-01
A numerical and theoretical study is presented for the propagation of electron Bernstein modes in a magnetized quantum plasma. The dispersion relation for electrostatic waves is derived, using a semiclassical Vlasov model for Fermi-Dirac distributed electrons. The dispersion relation is checked numerically with direct Vlasov simulations, where the wave energy is concentrated to the Bernstein modes as well as to the zero-frequency convective mode. Dispersion relations in the long wavelength limit are derived, including the upper hybrid dispersion relation for a degenerate quantum plasma.
Numerical and theoretical study of Bernstein modes in a magnetized quantum plasma
Eliasson, Bengt; Shukla, Padma K.
2008-10-15
A numerical and theoretical study is presented for the propagation of electron Bernstein modes in a magnetized quantum plasma. The dispersion relation for electrostatic waves is derived, using a semiclassical Vlasov model for Fermi-Dirac distributed electrons. The dispersion relation is checked numerically with direct Vlasov simulations, where the wave energy is concentrated to the Bernstein modes as well as to the zero-frequency convective mode. Dispersion relations in the long wavelength limit are derived, including the upper hybrid dispersion relation for a degenerate quantum plasma.
Pure quantum states of a neutrino with rotating spin in dense magnetized matter
NASA Astrophysics Data System (ADS)
Arbuzova, E. V.; Lobanov, A. E.; Murchikova, E. M.
2010-02-01
The problem of neutrino spin rotation in dense matter and in strong electromagnetic fields is solved in accordance with the basic principles of quantum mechanics. We obtain a complete system of wave functions for a massive Dirac neutrino with an anomalous magnetic moment which are the eigenfunctions of the kinetic momentum operator and have the form of nonspreading wave packets. These wave functions enable one to consider the states of neutrino with rotating spin as pure quantum states and can be used for calculating probabilities of various processes with the neutrino in the framework of the Furry picture.
Mogi, M. Yoshimi, R.; Yasuda, K.; Kozuka, Y.; Tsukazaki, A.; Takahashi, K. S.; Kawasaki, M.; Tokura, Y.
2015-11-02
Quantum anomalous Hall effect (QAHE), which generates dissipation-less edge current without external magnetic field, is observed in magnetic-ion doped topological insulators (TIs) such as Cr- and V-doped (Bi,Sb){sub 2}Te{sub 3}. The QAHE emerges when the Fermi level is inside the magnetically induced gap around the original Dirac point of the TI surface state. Although the size of gap is reported to be about 50 meV, the observable temperature of QAHE has been limited below 300 mK. We attempt magnetic-Cr modulation doping into topological insulator (Bi,Sb){sub 2}Te{sub 3} films to increase the observable temperature of QAHE. By introducing the rich-Cr-doped thin (1 nm) layers at the vicinity of both the surfaces based on non-Cr-doped (Bi,Sb){sub 2}Te{sub 3} films, we have succeeded in observing the QAHE up to 2 K. The improvement in the observable temperature achieved by this modulation-doping appears to be originating from the suppression of the disorder in the surface state interacting with the rich magnetic moments. Such a superlattice designing of the stabilized QAHE may pave a way to dissipation-less electronics based on the higher-temperature and zero magnetic-field quantum conduction.
Electron motion induced by magnetic pulse in a bilayer quantum wire
NASA Astrophysics Data System (ADS)
Chwiej, T.
2016-06-01
We consider theoretical stimulation of electron motion in a quantum wire by means of ultrashort magnetic pulses of time duration between several and a few tens of picoseconds. In our considerations, an electron is confined in a nanowire which consists of two vertically stacked tunnel-coupled layers. If a magnetic pulse pierces this nanowire and its direction is parallel to the plane established by the layers, and additionally, it is perpendicular to the wire's axis, then the eigenstates of a single electron energy operator for vertical direction are hybridized by the off-diagonal terms of the full Hamiltonian. These terms depend linearly on the momentum operator, which means that such magnetically forced hybridization may induce electron motion in a nanowire. The classical counterpart of this quantum-mechanical picture is a situation in which the rotational electric field generated by a time-varying magnetic field pushes the charge densities localized in the upper and lower layers in opposite directions. We have found, however, that for an asymmetric vertical confinement in a bilayer nanowire, the major part of the single electron density starts to move in the direction of the local electric field in its layer forcing the minority part to move in this direction as well. It results in coherent motion of both densities in a particular direction. We analyze the dynamics of such motion in dependence on the time characteristics of a magnetic pulse and discuss potential applications of this effect in the construction of a magnetic valve.
Singh, Saurabh Kumar; Rajaraman, Gopalan
2016-01-01
Single-molecule magnets represent a promising route to achieve potential applications such as high-density information storage and spintronics devices. Among others, 4d/5d elements such as Re(IV) ion are found to exhibit very large magnetic anisotropy, and inclusion of this ion-aggregated clusters yields several attractive molecular magnets. Here, using ab intio calculations, we unravel the source of giant magnetic anisotropy associated with the Re(IV) ions by studying a series of mononuclear Re(IV) six coordinate complexes. The low-lying doublet states are found to be responsible for large magnetic anisotropy and the sign of the axial zero-field splitting parameter (D) can be categorically predicted based on the position of the ligand coordination. Large transverse anisotropy along with large hyperfine interactions opens up multiple relaxation channels leading to a fast quantum tunnelling of the magnetization (QTM) process. Enhancing the Re-ligand covalency is found to significantly quench the QTM process. PMID:26883278
Singh, Saurabh Kumar; Rajaraman, Gopalan
2016-02-17
Single-molecule magnets represent a promising route to achieve potential applications such as high-density information storage and spintronics devices. Among others, 4d/5d elements such as Re(IV) ion are found to exhibit very large magnetic anisotropy, and inclusion of this ion-aggregated clusters yields several attractive molecular magnets. Here, using ab intio calculations, we unravel the source of giant magnetic anisotropy associated with the Re(IV) ions by studying a series of mononuclear Re(IV) six coordinate complexes. The low-lying doublet states are found to be responsible for large magnetic anisotropy and the sign of the axial zero-field splitting parameter (D) can be categorically predicted based on the position of the ligand coordination. Large transverse anisotropy along with large hyperfine interactions opens up multiple relaxation channels leading to a fast quantum tunnelling of the magnetization (QTM) process. Enhancing the Re-ligand covalency is found to significantly quench the QTM process.
Singh, Saurabh Kumar; Rajaraman, Gopalan
2016-01-01
Single-molecule magnets represent a promising route to achieve potential applications such as high-density information storage and spintronics devices. Among others, 4d/5d elements such as Re(IV) ion are found to exhibit very large magnetic anisotropy, and inclusion of this ion-aggregated clusters yields several attractive molecular magnets. Here, using ab intio calculations, we unravel the source of giant magnetic anisotropy associated with the Re(IV) ions by studying a series of mononuclear Re(IV) six coordinate complexes. The low-lying doublet states are found to be responsible for large magnetic anisotropy and the sign of the axial zero-field splitting parameter (D) can be categorically predicted based on the position of the ligand coordination. Large transverse anisotropy along with large hyperfine interactions opens up multiple relaxation channels leading to a fast quantum tunnelling of the magnetization (QTM) process. Enhancing the Re-ligand covalency is found to significantly quench the QTM process. PMID:26883278
An architecture for quantum computation with magnetically trapped Holmium atoms
NASA Astrophysics Data System (ADS)
Saffman, Mark; Hostetter, James; Booth, Donald; Collett, Jeffrey
2016-05-01
Outstanding challenges for scalable neutral atom quantum computation include correction of atom loss due to collisions with untrapped background gas, reduction of crosstalk during state preparation and measurement due to scattering of near resonant light, and the need to improve quantum gate fidelity. We present a scalable architecture based on loading single Holmium atoms into an array of Ioffe-Pritchard traps. The traps are formed by grids of superconducting wires giving a trap array with 40 μm period, suitable for entanglement via long range Rydberg gates. The states | F = 5 , M = 5 > and | F = 7 , M = 7 > provide a magic trapping condition at a low field of 3.5 G for long coherence time qubit encoding. The F = 11 level will be used for state preparation and measurement. The availability of different states for encoding, gate operations, and measurement, spectroscopically isolates the different operations and will prevent crosstalk to neighboring qubits. Operation in a cryogenic environment with ultra low pressure will increase atom lifetime and Rydberg gate fidelity by reduction of blackbody induced Rydberg decay. We will present a complete description of the architecture including estimates of achievable performance metrics. Work supported by NSF award PHY-1404357.
Lyo, S.K.; Harff, N.E.; Simmons, J.A.
1998-07-01
We present a linear-response theory of magneto-quantum-resistance oscillations of the in-plane resistances R{sub xx} and R{sub yy} in two coupled quasi-two-dimensional electron layers in tilted magnetic fields {bold B}=(B{sub {parallel}},B{sub {perpendicular}}), and explain recent data from GaAs/Al{sub x}Ga{sub 1{minus}x}As double quantum wells. In this system, the electrons are in the two tunnel-split ground sublevels. The cyclotron masses of the two orbits on the Fermi surface have opposite dependences on the in-plane field B{sub {parallel}}: one increases monotonically, while the other decreases as a function of B{sub {parallel}} in the regime of interest. As a result, the rungs of one Landau ladder sweep up through the Fermi level, while those of the other Landau ladder sweep down when B{sub {parallel}} is increased at a fixed perpendicular field B{sub {perpendicular}}. Ridges are obtained in the three-dimensional plots of both R{sub xx} and R{sub yy} and the density of states versus (B{sub {parallel}},B{sub {perpendicular}}) due to Fermi-level crossing by the rungs of the Landau ladders. Giant peaks are obtained when two ridges intersect each other. The (B{sub {parallel}},B{sub {perpendicular}}) dependence of R{sub xx} as well as theoretical evidence of magnetic breakdown yields good agreement with recent data from GaAs/Al{sub x}Ga{sub 1{minus}x}As double quantum wells. {copyright} {ital 1998} {ital The American Physical Society}
Magnetic moments of light nuclei from lattice quantum chromodynamics
Beane, S. R.; Chang, E.; Cohen, S.; Detmold, W.; Lin, H. W.; Orginos, K.; Parreño, A.; Savage, M. J.; Tiburzi, B. C.
2014-12-16
We present the results of lattice QCD calculations of the magnetic moments of the lightest nuclei, the deuteron, the triton and ^{3}He, along with those of the neutron and proton. These calculations, performed at quark masses corresponding to m_{π} ~ 800 MeV, reveal that the structure of these nuclei at unphysically heavy quark masses closely resembles that at the physical quark masses. We find that the magnetic moment of ^{3}He differs only slightly from that of a free neutron, as is the case in nature, indicating that the shell-model configuration of two spin-paired protons and a valence neutron captures its dominant structure. Similarly a shell-model-like moment is found for the triton, μ_{3H} ~ μ_{p}. The deuteron magnetic moment is found to be equal to the nucleon isoscalar moment within the uncertainties of the calculations.
NASA Astrophysics Data System (ADS)
Binz, Ernst; Schempp, Walter
2001-06-01
Quantum holography is a well established theory of mathematical physics based on harmonic analysis on the Heisenberg Lie group G. The geometric quantization is performed by projectivization of the complexified coadjoint orbit picture of the unitary dual Ĝ of G in order to achieve a geometric adjustment of the quantum scenario to special relativity theory. It admits applications to various imaging modalities such as synthetic aperture radar (SAR) in the microwave range, and, most importantly for the field of non-invasive medical diagnosis, to the clinical imaging modality of magnetic resonance tomography (MRI) in the radio frequency range. Quantum holography explains the quantum teleportation phenomemon through Einstein-Podolsky-Rosen (EPR) channels which is a consequence of the non-locality of phase coherent quantum field theory, the concept of absolute simultaneity of special relativity theory which provides the Einstein equivalence of energy and Fitzgerald-Lorentz dilated mass, and the perfect quantum holographic replication process of molecular genetic information processing. It specifically reveals what was before unobservable in quantum optics, namely the interference phenomena of matter wavelets of Bose-Einstein condensates, and what was before unobservable in special relativity, namely the light in flight (LIF) recording processing by ultrafast laser pulse trains. Finally, it provides a Lie group theoretical approach to the Kruskal coordinatized Schwarzschild manifold of relativistic cosmology with large scale applications to general relativity theory such as gravitational instanton symmetries and the theory of black holes. The direct spinorial detection of gravitational wavelets emitted by the binary radio pulsar PSR 1913+16 and known only by anticipatory system computation so far will also be based on the principles of quantum holography applied to very large array (VLA) radio interferometers. .
Quantum phase transitions in holographic models of magnetism and superconductors
Iqbal, Nabil; Liu Hong; Mezei, Mark; Si Qimiao
2010-08-15
We study a holographic model realizing an 'antiferromagnetic' phase in which a global SU(2) symmetry representing spin is broken down to a U(1) by the presence of a finite electric charge density. This involves the condensation of a neutral scalar field in a charged anti-de Sitter black hole. We observe that the phase transition for both neutral and charged (as in the standard holographic superconductor) order parameters can be driven to zero temperature by a tuning of the UV conformal dimension of the order parameter, resulting in a quantum phase transition of the Berezinskii-Kosterlitz-Thouless-type. We also characterize the antiferromagnetic phase and an externally forced ferromagnetic phase by showing that they contain the expected spin waves with linear and quadratic dispersions, respectively.
Investigations of pressure induced structural phase transformations in pentaerythritol
NASA Astrophysics Data System (ADS)
Garg, Nandini; Sharma, Surinder M.; Sikka, S. K.
2005-10-01
We have investigated the pressure induced structural changes in pentaerythritol {2,2-bis-(hydroxymethyl)-1,3-propanediol} with the help of X-ray diffraction studies. Our results show that this compound undergoes transformations to a lower symmetry phase between 5.2-5.9 GPa. It further undergoes phase transformations at ˜8.5 and ˜11 GPa; eventually evolving to a disordered phase beyond 14-15 GPa in agreement with our earlier Raman studies. On release of pressure from 18.5 GPa, the compound transforms back to the initial tetragonal phase.
Magnon Hall effect in AB-stacked bilayer honeycomb quantum magnets
NASA Astrophysics Data System (ADS)
Owerre, S. A.
2016-09-01
Motivated by the fact that many bilayer quantum magnets occur in nature, we generalize the study of thermal Hall transports of spin excitations to bilayer magnetic systems. It is shown that bilayer magnetic systems can be coupled either ferromagnetically or antiferromagnetically. We study both scenarios on the honeycomb lattice and show that the system realizes topologically nontrivial magnon bands induced by alternating next-nearest-neighbor Dzyaloshinsky-Moriya interaction. As a result, the bilayer system realizes both magnon Hall effect and magnon spin Nernst effect. We show that antiferromagnetically coupled layers differ from ferromagnetically coupled layers by a sign change in the conductivities as the magnetic field is reversed. Furthermore, Chern number protected magnon edge states are observed and propagate in the same direction on the top and bottom layers in ferromagnetically coupled layers, whereas the magnon edge states propagate in opposite directions for antiferromagnetically coupled layers.
Kumar, D. Sanjeev Chatterjee, Ashok; Mukhopadhyay, Soma
2015-05-15
The magnetization of a parabolic quantum dot has been studied as a function of temperature and external magnetic field in the presence of Rashba, Dresselhaus Spin Orbit Interactions (SOI) and the electron-electron interactions. By the introduction of a simple and physically reasonable model potential, the problem has been solved exactly up to second order in both the SOI terms. Both the SOI found to be showing considerable effects on the magnetization of the quantum dot. The effect of electron-electron interaction on the magnetization also has been studied.
NASA Astrophysics Data System (ADS)
Boda, Aalu; Kumar, D. Sanjeev; Sankar, I. V.; Chatterjee, Ashok
2016-11-01
The problem of a parabolically confined two-dimensional semiconductor GaAs quantum dot with two interacting electrons in the presence of an external magnetic field and the spin-Zeeman interaction is studied using a method of numerical diagonalization. The energy spectrum is calculated as a function of the magnetic field. The magnetic moment (M) and the magnetic susceptibility (χ) show zero temperature diamagnetic peaks due to the exchange induced singlet-triplet transitions. The position and the number of these peaks depend both on the confinement strength of the quantum dot and the strength of the electron-electron interaction (β) .
Electric field control of spin splitting in III-V semiconductor quantum dots without magnetic field
NASA Astrophysics Data System (ADS)
Prabhakar, Sanjay; Melnik, Roderick
2015-10-01
We provide an alternative means of electric field control for spin manipulation in the absence of magnetic fields by transporting quantum dots adiabatically in the plane of two-dimensional electron gas. We show that the spin splitting energy of moving quantum dots is possible due to the presence of quasi-Hamiltonian that might be implemented to make the next generation spintronic devices of post CMOS technology. Such spin splitting energy is highly dependent on the material properties of semiconductor. It turns out that this energy is in the range of meV and can be further enhanced with increasing pulse frequency. In particular, we show that quantum oscillations in phonon mediated spin-flip behaviors can be observed. We also confirm that no oscillations in spin-flip behaviors can be observed for the pure Rashba or pure Dresselhaus cases.
Quantum critical dynamics of a magnetic impurity in a semiconducting host
NASA Astrophysics Data System (ADS)
Dasari, Nagamalleswararao; Acharya, Swagata; Taraphder, A.; Moreno, Juana; Jarrell, Mark; Vidhyadhiraja, N. S.; N. S. Vidhyadhiraja Collaboration, Prof.; Mark Jarrell Collaboration, Prof.; A. Taraphder Collaboration, Prof.
We have investigated the finite temperature dynamics of the singlet to doublet continuous quantum phase transition in the gapped Anderson impurity model using hybridization expansion continuous time quantum Monte Carlo. Using the self-energy and the longitudinal static susceptibility, we obtain a phase diagram in the temperature-gap plane. The separatrix between the low-temperature local moment phase and the high temperature generalized Fermi liquid phase is shown to be the lower bound of the critical scaling region of the zero gap interacting quantum critical point. We have computed the nuclear magnetic spin-lattice relaxation rate, the Knight shift, and the Korringa ratio, which show strong deviations for any non-zero gap from the corresponding quantities in the gapless Kondo screened impurity case. This work is supported by NSF DMR-1237565 and NSF EPSCoR Cooperative Agreement EPS-1003897 with additional support from the Louisiana Board of Regents, and by CSIR and DST, India.
Magnetic and Ising quantum phase transitions in a model for isoelectronically tuned iron pnictides
NASA Astrophysics Data System (ADS)
Wu, Jianda; Si, Qimiao; Abrahams, Elihu
2016-03-01
Considerations of the observed bad-metal behavior in Fe-based superconductors led to an early proposal for quantum criticality induced by isoelectronic P for As doping in iron arsenides, which has since been experimentally confirmed. We study here an effective model for the isoelectronically tuned pnictides using a large-N approach. The model contains antiferromagnetic and Ising-nematic order parameters appropriate for J1-J2 exchange-coupled local moments on an Fe square lattice, and a damping caused by coupling to itinerant electrons. The zero-temperature magnetic and Ising transitions are concurrent and essentially continuous. The order-parameter jumps are very small, and are further reduced by the interplane coupling; consequently, quantum criticality occurs over a wide dynamical range. Our results reconcile recent seemingly contradictory experimental observations concerning the quantum phase transition in the P-doped iron arsenides.
Screening of the Coulomb field in a magnetized electron gas of a quantum cylinder
Eminov, P. A.
2009-05-15
The quantum theory is constructed for screening of the Coulomb field of a point charge in a magnetized electron gas of a quantum cylinder. The asymptotics of the screened potential are calculated for both degenerate and Boltzmann electron gases. It is demonstrated that, in the degenerate case, apart from the known quasi-classical monotonic part, the result contains the quantum oscillating part, which corresponds to Friedel oscillations. The Aharonov-Bohm oscillations of the screened Coulomb interaction of electrons on a cylindrical surface are described analytically. It is shown that the Friedel oscillations can be represented as a superposition of oscillations with different frequencies which are determined by the macroscopic properties of the nanotube.
Search for pressure-induced superconductivity in CeFeAsO and CeFePO iron pnictides
Zocco, D. A.; Baumbach, R. E.; Hamlin, J. J.; Janoschek, M.; Lum, I. K.; McGuire, Michael A; Safa-Sefat, Athena; Sales, Brian C; Jin, Rongying; Mandrus, David; Jeffries, J. R.; Weir, S. T.; Vohra, Y. K.; Maple, M. B.
2011-01-01
The CeFeAsO and CeFePO iron pnictide compounds were studied via electrical transport measurements under high pressure. In CeFeAsO polycrystals, the magnetic phases involving the Fe and Ce ions coexist for hydrostatically applied pressures up to 15 GPa, and with no signs of pressure-induced superconductivity up to 50 GPa for the less hydrostatic pressure techniques. For the CeFePO single crystals, pressure further stabilizes the Kondo screening of the Ce 4f-electron magnetic moments.
Magnetic field tuned quantum criticality of heavy fermion system YbPtBi
NASA Astrophysics Data System (ADS)
Mun, Eundeok
2014-03-01
Quantum criticality triggers an emergence of new quantum phase of matters due to the critical behavior of quantum fluctuations. Heavy fermion (HF) compounds have provided the cleanest evidence for the quantum phase transition. The face-centered cubic YbPtBi is one of the few frustrated stoichiometric Yb-based HF compounds. Measurements of magnetic field and temperature dependent resistivity, specific heat, thermal expansion, Hall effect, and thermoelectric power indicate that the antiferromagnetic (AFM) order (TN ~ 0.4 K) can be suppressed by applied magnetic field of Hc ~ 4 kOe. In the H- T phase diagram of YbPtBi, three regimes of its low temperature states emerges: (I) AFM state, characterized by spin density wave (SDW) 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 ρ(T) ~T 1 . 5 between Hc and ~ 8 kOe, and (III) Fermi liquid (FL) state in which ρ(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 4 f states of Yb, region II may be a manifestation of a spin liquid state. Work was supported by the US Department of Energy, Office of Basic Energy Science, Division of Materials Sciences and Engineering. Ames Laboratory is operated for the US Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358.
Electrically detected nuclear magnetic resonance in GaAs/AlGaAs-based quantum point contacts
NASA Astrophysics Data System (ADS)
Keane, Zachary; Godfrey, Matthew; Burke, Adam; Chen, Jason; Fricke, Sebastian; Klochan, Oleh; Micolich, Adam; Beere, Harvey; Ritchie, Dave; Trunov, Kirill; Reuter, Dirk; Wieck, Andreas; Hamilton, Alex
2011-03-01
Nuclear magnetic resonance (NMR) is a well-known technique with widespread applications in physics, chemistry and medicine. Conventional NMR studies use inductive coils to detect the magnetic field produced by precessing nuclear spins; this approach requires on the order of 1012 spins for detection. Recently, resistive detection of NMR through the hyperfine interaction has been demonstrated with electrons in mesoscopic 2- and 1-dimensional devices based on high-quality GaAs/AlGaAs heterostructures. These studies are typically sensitive to 108 spins, enabling NMR on much smaller sample volumes. Holes are predicted to have much weaker nuclear spin coupling than electrons, which could be relevant to the emerging fields of spintronics and quantum information processing. We present a preliminary comparison between the magnitude of the NMR signal in electron and hole quantum point contacts.
Fu, Zhen-Guo; Zhang, Ping; Wang, Zhigang; Li, Shu-Shen
2012-04-11
We theoretically study the effect of localized magnetic impurities on two-dimensional topological superconductor (TSC). We show that the local density of states (LDOS) can be tuned by the effective exchange field m, the chemical potential μ of TSC, and the distance Δr as well as the relative spin angle α between two impurities. The changes in Δr between two impurities alter the interference and result in significant modifications to the bonding and antibonding states. Furthermore, the bound-state spin LDOS induced by single and double magnetic impurity scattering, the quantum corrals and the quantum mirages are also discussed. Finally, we briefly compare the impurities in TSC with those in topological insulators.
Quantum logic gates from time-dependent global magnetic field in a system with constant exchange
Nenashev, A. V. Dvurechenskii, A. V.; Zinovieva, A. F.; Gornov, A. Yu.; Zarodnyuk, T. S.
2015-03-21
We propose a method that implements a universal set of one- and two-quantum-bit gates for quantum computation in a system of coupled electron pairs with constant non-diagonal exchange interaction. In our proposal, suppression of the exchange interaction is performed by the continual repetition of single-spin rotations. A small g-factor difference between the electrons allows for addressing qubits and avoiding strong magnetic field pulses. Numerical experiments were performed to show that, to implement the one- and two-qubit operations, it is sufficient to change the strength of the magnetic field by a few Gauss. This introduces one and then the other electron in a resonance. To determine the evolution of the two-qubit system, we use the algorithms of optimal control theory.
Magnetic breakdown and Landau level spectra of a tunable double-quantum-well Fermi surface
Simmons, J.A.; Harff, N.E.; Lyo, S.K.; Klem, J.F.; Boebinger, G.S.; Pfeiffer, L.N.; West, K.W.
1997-12-31
By measuring longitudinal resistance, the authors map the Landau level spectra of double quantum wells as a function of both parallel (B{sub {parallel}}) and perpendicular (B{sub {perpendicular}}) magnetic fields. In this continuously tunable highly non-parabolic system, the cyclotron masses of the two Fermi surface orbits change in opposite directions with B{sub {parallel}}. This causes the two corresponding ladders of Landau levels formed at finite B{sub {perpendicular}} to exhibit multiple crossings. They also observe a third set of landau levels, independent of B{sub {parallel}}, which arise from magnetic breakdown of the Fermi surface. Both semiclassical and full quantum mechanical calculations show good agreement with the data.
Magnetically tunable Kondo-Aharonov-Bohm effect in a triangular quantum dot.
Kuzmenko, T; Kikoin, K; Avishai, Y
2006-02-01
The role of discrete orbital symmetry in mesoscopic physics is manifested in a system consisting of three identical quantum dots forming an equilateral triangle. Under a perpendicular magnetic field, this system demonstrates a unique combination of Kondo and Aharonov-Bohm features due to an interplay between continuous [spin-rotation SU(2)] and discrete (permutation C3v) symmetries, as well as U(1) gauge invariance. The conductance as a function of magnetic flux displays sharp enhancement or complete suppression depending on contact setups.
Field-dependent superradiant quantum phase transition of molecular magnets in microwave cavities
NASA Astrophysics Data System (ADS)
Stepanenko, Dimitrije; Trif, Mircea; Tsyplyatyev, Oleksandr; Loss, Daniel
2016-09-01
We study a superradiant quantum phase transition in the model of triangular molecular magnets coupled to the electric component of a microwave cavity field. The transition occurs when the coupling strength exceeds a critical value, d c, which, in sharp contrast to the standard two-level emitters, can be tuned by an external magnetic field. In addition to emitted radiation, the molecules develop an in-plane electric dipole moment at the transition. We estimate that the transition can be detected in state-of-the-art microwave cavities if their electric field couples to a crystal containing a sufficient number of oriented molecules.
Magnetic field effect on the Coulomb interaction of acceptors in semimagnetic quantum dot
Kalpana, P.; Merwyn, A.; Nithiananthi, P.; Jayakumar, K.; Reuben, Jasper D.
2015-06-24
The Coulomb interaction of holes in a Semimagnetic Cd{sub 1-x}Mn{sub x}Te / CdTe Spherical and Cubical Quantum Dot (SMQD) in a magnetic field is studied using variational approach in the effective mass approximation. Since these holes in QD show a pronounced collective behavior, while distinct single particle phenomena is suppressed, their interaction in confined potential becomes very significant. It has been observed that acceptor-acceptor interaction is more in cubical QD than in spherical QD which can be controlled by the magnetic field. The results are presented and discussed.
Magnetic forces and localized resonances in electron transfer through quantum rings
NASA Astrophysics Data System (ADS)
Poniedziałek, M. R.; Szafran, B.
2010-11-01
We study the current flow through semiconductor quantum rings. In high magnetic fields the current is usually injected into the arm of the ring preferred by classical magnetic forces. However, for narrow magnetic field intervals that appear periodically on the magnetic field scale the current is injected into the other arm of the ring. We indicate that the appearance of the anomalous—non-classical—current circulation results from Fano interference involving localized resonant states. The identification of the Fano interference is based on the comparison of the solution of the scattering problem with the results of the stabilization method. The latter employs the bound-state type calculations and allows us to extract both the energy of metastable states localized within the ring and the width of resonances by analysis of the energy spectrum of a finite size system as a function of its length. The Fano resonances involving states of anomalous current circulation become extremely narrow on both the magnetic field and energy scales. This is consistent with the orientation of the Lorentz force that tends to keep the electron within the ring and thus increases the lifetime of the electron localization within the ring. Absence of periodic Fano resonances in electron transfer probability through a quantum ring containing an elastic scatterer is also explained.
Space-charge waves in magnetized and collisional quantum plasma columns confined in carbon nanotubes
Bagheri, Mehran; Abdikian, Alireza
2014-04-15
We study the dispersion relation of electrostatic waves propagating in a column of quantum magnetized collisional plasma embraced completely by a metallic single-walled carbon nanotubes. The analysis is based on the quantum linearized hydrodynamic formalism of collective excitations within the quasi-static approximation. It is shown when the electronic de Broglie's wavelength of the plasma is comparable in the order of magnitude to the radius of the nanotube, the quantum effects are quite meaningful and our model anticipates one acoustical and two optical space-charge waves which are positioned into three propagating bands. With increasing the nanotube radius, the features of the acoustical branch remain unchanged, yet two distinct optical branches are degenerated and the classical behavior is recovered. This study might provide a platform to create new finite transverse cross section quantum magnetized plasmas and to devise nanometer dusty plasmas based on the metallic carbon nanotubes in the absence of either a drift or a thermal electronic velocity and their existence could be experimentally examined.
Yamamoto, Daisuke; Marmorini, Giacomo; Danshita, Ippei
2015-01-16
Magnetization processes of spin-1/2 layered triangular-lattice antiferromagnets (TLAFs) under a magnetic field H are studied by means of a numerical cluster mean-field method with a scaling scheme. We find that small antiferromagnetic couplings between the layers give rise to several types of extra quantum phase transitions among different high-field coplanar phases. Especially, a field-induced first-order transition is found to occur at H≈0.7H_{s}, where H_{s} is the saturation field, as another common quantum effect of ideal TLAFs in addition to the well-established one-third plateau. Our microscopic model calculation with appropriate parameters shows excellent agreement with experiments on Ba_{3}CoSb_{2}O_{9} [T. Susuki et al., Phys. Rev. Lett. 110, 267201 (2013)]. Given this fact, we suggest that the Co^{2+}-based compounds may allow for quantum simulations of intriguing properties of this simple frustrated model, such as quantum criticality and supersolid states. PMID:25635561
Hybrid-impurity resonance in a quantum wire placed in a magnetic field
NASA Astrophysics Data System (ADS)
Karpunin, V. V.; Margulis, V. A.
2016-09-01
An analytical expression for the absorption coefficient of electromagnetic radiation in a quantum wire is obtained. We consider the case of a field lying in the plane perpendicular to the wire axis. The calculation is performed using second-order perturbation theory with consideration of electron scattering by ionized impurities. We demonstrate the resonant character of the absorption and find the position of resonance frequencies in the dependence on the magnitude and direction of the magnetic field.
Triple-quantum-filtered sodium magnetic resonance imaging
NASA Astrophysics Data System (ADS)
Hancu, Ileana
2001-11-01
In this thesis, a method to selectively detect sodium ions in slow motion, the triple-quantum (TQ) filtering technique, was implemented for the first time in a whole- body, clinical MR scanner. The method was used for collecting images from in vivo normal and neoplastic human brain tissues, and cartilage tissue. It was confirmed that the TQ filter rejects signals from liquid-like environments, and it became apparent that this method might become useful for the diagnosis and prognosis of brain neoplasms. Additional issues related to implementing a TQ filter in clinical scanners were considered. The effect of B1 and B0 imperfections was analyzed for the three- and four-pulse TQ filters. It was concluded that the signal loss due to B1 inhomogeneities in the four-pulse filter could be overwhelmingly high if flip angles are not perfect. The three-pulse filter leads to much smaller signal losses, and has the advantage that signal biases can be corrected for by post-processing. The effect of relaxation during the application of RF pulses was also considered. Since pulse-widths normally used for hard 90-degree pulses in clinical scanners are comparable to the relaxation times of sodium ions, the amount of TQ-filtered signal loss due to this effect was checked, theoretically and experimentally. By increasing the pulse width of the hard 90-degree RF pulses from 100μs to 500μs in a cartilage sample, about 15% of the TQ-signal is lost, therefore shorter pulses will not dramatically increase the TQ-filtered signal strength. A new method to selectively detect sodium ions in anisotropic environments was also developed. Following the application of a hard 90-degree pulse, quadrupolar polarization is created during the application of a spin- lock (SL) field only in the presence of residual quadrupolar couplings (if B1 is on the same order of magnitude with these couplings). This coherence is then converted into observable signal by a coherence- transfer pulse. The SL-filter has
Quantum tunneling of two coupled single-molecular magnets
NASA Astrophysics Data System (ADS)
Hu, Jianming; Chen, Zhide; Shen, Shunqing
2003-03-01
Jian-Ming Hu, Zhi-De Chen and Shun-Qing Shen Department of Physics, The University of Hong Kong Pokfulam Road, Hong Kong December 02, 2002 Very recently a supramolecular dimer of two single-molecule magnets (SMM) was reported to be synthesized successfully. Two single-molecule magnets are coupled antiferromagnetically to form a supramolecule dimer. We study the coupling effect and tunneling process by the numerical exact diagonalization method. The sweeping rate effect in the derivatives of hysteresis loops has been quantitatively investigated using the modified Landau-Zener model. In addiction we find that exchange coupling between the two SMMs provides a biased field to expel the tunneling between SMMs to two new resonant points via an intermediate state, and direct tunneling is prohibited. The model parameters are calculated for the dimer based on the tunneling process. The outcome indicates that the coupling effect will not change the parameters of each SMM too much at all. This work is supported by a CRCG grant of The University of Hong Kong.
NASA Astrophysics Data System (ADS)
Abdullah, Nzar Rauf; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar
2016-09-01
We investigate theoretically the balance of the static magnetic and the dynamical photon forces in the electron transport through a quantum dot in a photon cavity with a single photon mode. The quantum dot system is connected to external leads and the total system is exposed to a static perpendicular magnetic field. We explore the transport characteristics through the system by tuning the ratio, \\hslash {ωγ}/\\hslash {ωc} , between the photon energy, \\hslash {ωγ} , and the cyclotron energy, \\hslash {ωc} . Enhancement in the electron transport with increasing electron-photon coupling is observed when \\hslash {ωγ}/\\hslash {ωc}>1 . In this case the photon field dominates and stretches the electron charge distribution in the quantum dot, extending it towards the contact area for the leads. Suppression in the electron transport is found when \\hslash {ωγ}/\\hslash {ωc}<1 , as the external magnetic field causes circular confinement of the charge density around the dot.
A quantum description of radiation damping and the free induction signal in magnetic resonance
Tropp, James
2013-07-07
We apply the methods of cavity quantum electrodynamics (CQED), to obtain a microscopic and fully quantum-mechanical picture of radiation damping in magnetic resonance, and the nascent formation of the free induction signal. Numerical solution of the Tavis-Cummings model - i.e., multiple spins 1/2 coupled to a lossless single-mode cavity - shows in fine detail the transfer of Zeeman energy, via spin coherence, to excite the cavity - represented here by a quantized LC resonator. The case of a single spin is also solved analytically. Although the motion of the Bloch vector is non-classical, we nonetheless show that the quantum mechanical Rabi nutation frequency (as enhanced by cavity coupling and stimulated emission) gives realistic estimates of macroscopic signal strength and the radiation damping constant in nuclear magnetic resonance. We also show how to introduce dissipation: cavity losses by means of a master equation, and relaxation by the phenomenological method of Bloch. The failure to obtain the full Bloch equations (unless semi-classical conditions are imposed on the cavity) is discussed in light of similar issues arising in CQED (and in earlier work in magnetic resonance as well), as are certain problems relative to quantization of the electromagnetic near-field.
NASA Astrophysics Data System (ADS)
Abdullah, Nzar Rauf; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar
2016-09-01
We investigate theoretically the balance of the static magnetic and the dynamical photon forces in the electron transport through a quantum dot in a photon cavity with a single photon mode. The quantum dot system is connected to external leads and the total system is exposed to a static perpendicular magnetic field. We explore the transport characteristics through the system by tuning the ratio, \\hslash {ωγ}/\\hslash {ωc} , between the photon energy, \\hslash {ωγ} , and the cyclotron energy, \\hslash {ωc} . Enhancement in the electron transport with increasing electron–photon coupling is observed when \\hslash {ωγ}/\\hslash {ωc}>1 . In this case the photon field dominates and stretches the electron charge distribution in the quantum dot, extending it towards the contact area for the leads. Suppression in the electron transport is found when \\hslash {ωγ}/\\hslash {ωc}<1 , as the external magnetic field causes circular confinement of the charge density around the dot.
A quantum description of radiation damping and the free induction signal in magnetic resonance.
Tropp, James
2013-07-01
We apply the methods of cavity quantum electrodynamics (CQED), to obtain a microscopic and fully quantum-mechanical picture of radiation damping in magnetic resonance, and the nascent formation of the free induction signal. Numerical solution of the Tavis-Cummings model - i.e., multiple spins 1∕2 coupled to a lossless single-mode cavity - shows in fine detail the transfer of Zeeman energy, via spin coherence, to excite the cavity - represented here by a quantized LC resonator. The case of a single spin is also solved analytically. Although the motion of the Bloch vector is non-classical, we nonetheless show that the quantum mechanical Rabi nutation frequency (as enhanced by cavity coupling and stimulated emission) gives realistic estimates of macroscopic signal strength and the radiation damping constant in nuclear magnetic resonance. We also show how to introduce dissipation: cavity losses by means of a master equation, and relaxation by the phenomenological method of Bloch. The failure to obtain the full Bloch equations (unless semi-classical conditions are imposed on the cavity) is discussed in light of similar issues arising in CQED (and in earlier work in magnetic resonance as well), as are certain problems relative to quantization of the electromagnetic near-field.
Quantum speed limit for a relativistic electron in a uniform magnetic field
NASA Astrophysics Data System (ADS)
Villamizar, D. V.; Duzzioni, E. I.
2015-10-01
We analyze the influence of relativistic effects on the minimum evolution time between two orthogonal states of a quantum system. Defining the initial state as a homogeneous superposition between two Hamiltonian eigenstates of an electron in a uniform magnetic field, we obtain a relation between the minimum evolution time and the displacement of the mean radial position of the electron wave packet. The quantum speed limit time is calculated for an electron dynamics described by Dirac and Schrödinger-Pauli equations considering different parameters, such as the strength of magnetic field and the linear momentum of the electron in the axial direction. We highlight that when the electron undergoes a region with extremely strong magnetic field the relativistic and nonrelativistic dynamics differ substantially, so that the description given by the Schrödinger-Pauli equation enables the electron to travel faster than c , which is prohibited by Einstein's theory of relativity. This approach allows a connection between the abstract Hilbert space and the space-time coordinates, besides the identification of the most appropriate quantum dynamics used to describe the electron motion.
Wavefunction dynamics in a quantum-dot electron pump under a high magnetic field
NASA Astrophysics Data System (ADS)
Ryu, Sungguen; Kataoka, Masaya; Sim, Heung-Sun
2015-03-01
A quantum-dot electron pump, formed and operated by applying time-dependent potential barriers to a two dimensional electron gas system, provides a promising redefinition of ampere. The pump operation consists of capturing an electron from a reservoir into a quantum dot and ejecting it to another reservoir. The capturing process has been theoretically understood by a semi-classical treatment of the tunneling between the dot and reservoir. But the dynamics of the wavefunction of the captured electron in the ejection process has not been theoretically addressed, although it is useful for enhancing pump accuracy and for utilizing the pump as a single-electron source for mesoscopic quantum electron devices. We study the dynamics under a strong magnetic field that leads to magnetic confinement of the captured electron, which dominates over the electrostatic confinement of the dot. We find that the wave packet of the captured electron has the Gaussian form with the width determined by the strength of the magnetic field, and that the time evolution of the packet follows the classical drift motion, with maintaining the Gaussian form. We discuss the possible signatures of the wave packet dynamics in experiments.
Magnetic-Field-Assisted Terahertz Quantum Cascade Laser Operating up to 225 K
NASA Technical Reports Server (NTRS)
Wade, A.; Fedorov, G.; Smirnov, D.; Kumar, S.; Williams, B. S.; Hu, Q.; Reno, J. L.
2008-01-01
Advances in semiconductor bandgap engineering have resulted in the recent development of the terahertz quantum cascade laser1. These compact optoelectronic devices now operate in the frequency range 1.2-5 THz, although cryogenic cooling is still required2.3. Further progress towards the realization of devices operating at higher temperatures and emitting at longer wavelengths (sub-terahertz quantum cascade lasers) is difficult because it requires maintaining a population inversion between closely spaced electronic sub-bands (1 THz approx. equals 4 meV). Here, we demonstrate a magnetic-field-assisted quantum cascade laser based on the resonant-phonon design. By applying appropriate electrical bias and strong magnetic fields above 16 T, it is possible to achieve laser emission from a single device over a wide range of frequencies (0.68-3.33 THz). Owing to the suppression of inter-landau-level non-radiative scattering, the device shows magnetic field assisted laser action at 1 THz at temperatures up to 215 K, and 3 THz lasing up to 225 K.
Irreversibility of pressure induced boron speciation change in glass.
Smedskjaer, Morten M; Youngman, Randall E; Striepe, Simon; Potuzak, Marcel; Bauer, Ute; Deubener, Joachim; Behrens, Harald; Mauro, John C; Yue, Yuanzheng
2014-01-01
It is known that the coordination number (CN) of atoms or ions in many materials increases through application of sufficiently high pressure. This also applies to glassy materials. In boron-containing glasses, trigonal BO3 units can be transformed into tetrahedral BO4 under pressure. However, one of the key questions is whether the pressure-quenched CN change in glass is reversible upon annealing below the ambient glass transition temperature (Tg). Here we address this issue by performing (11)B NMR measurements on a soda lime borate glass that has been pressure-quenched at ~0.6 GPa near Tg. The results show a remarkable phenomenon, i.e., upon annealing at 0.9Tg the pressure-induced change in CN remains unchanged, while the pressurised values of macroscopic properties such as density, refractive index, and hardness are relaxing. This suggests that the pressure-induced changes in macroscopic properties of soda lime borate glasses compressed up to ~0.6 GPa are not attributed to changes in the short-range order in the glass, but rather to changes in overall atomic packing density and medium-range structures.
Irreversibility of Pressure Induced Boron Speciation Change in Glass
Smedskjaer, Morten M.; Youngman, Randall E.; Striepe, Simon; Potuzak, Marcel; Bauer, Ute; Deubener, Joachim; Behrens, Harald; Mauro, John C.; Yue, Yuanzheng
2014-01-01
It is known that the coordination number (CN) of atoms or ions in many materials increases through application of sufficiently high pressure. This also applies to glassy materials. In boron-containing glasses, trigonal BO3 units can be transformed into tetrahedral BO4 under pressure. However, one of the key questions is whether the pressure-quenched CN change in glass is reversible upon annealing below the ambient glass transition temperature (Tg). Here we address this issue by performing 11B NMR measurements on a soda lime borate glass that has been pressure-quenched at ~0.6 GPa near Tg. The results show a remarkable phenomenon, i.e., upon annealing at 0.9Tg the pressure-induced change in CN remains unchanged, while the pressurised values of macroscopic properties such as density, refractive index, and hardness are relaxing. This suggests that the pressure-induced changes in macroscopic properties of soda lime borate glasses compressed up to ~0.6 GPa are not attributed to changes in the short-range order in the glass, but rather to changes in overall atomic packing density and medium-range structures. PMID:24442182
Scaling of the magnetic Grüneisen ratio near quantum critical point
NASA Astrophysics Data System (ADS)
Tokiwa, Yoshi
2014-03-01
The magnetic Grüneisen ratio ΓH = (1/T)dT/dH is the most sensitive probe of quantum criticality. Its divergence signals the underlying instability. We have studied quantum criticality in the frustrated Kondo lattice system YbAgGe and the heavy fermion superconductor CeCoIn5 by high-precision magnetocaloric effect measurements. In the former, NFL behavior appears around a metamagnetic spin-flop transition between two symmetry broken phases. Previously, it was unclear how the two ordered phases are related to the NFL state. Here, we propose a novel quantum bicritical point (QBCP) scenario, which is distinct from either quantum critical end point or ordinary QCPs with single symmetry broken phase. The observed scaling behavior of ΓH and its characteristic asymmetry across the critical field are consistent with a QBCP scenario. We also report a possible violation of Wiedemann-Franz law at the QBCP in YbAgGe. In CeCoIn5 indications of a quantum critical field hidden inside the superconducting (SC) phase have been extensively debated. We show ΓH data and scaling analysis in the normal state, which surprisingly suggests a zero-field QCP. Anomalous behaviors of ΓH and specific heat within the SC state further support this conclusion.
Observation of the transition state for pressure-induced BO₃→ BO₄ conversion in glass.
Edwards, Trenton; Endo, Takatsugu; Walton, Jeffrey H; Sen, Sabyasachi
2014-08-29
A fundamental mechanistic understanding of the pressure- and/or temperature-induced facile transformation of the coordination environment of boron is important for changing the physical properties of glass. We have used in situ high-pressure (up to 2 gigapascals) boron-11 solid-state nuclear magnetic resonance spectroscopy in combination with ab initio calculations to investigate the nature of the transition state for the pressure-induced BO3→ BO4 conversion in a borosilicate glass at ambient temperature. The results indicate an anisotropic elastic deformation of the BO3 planar triangle, under isotropic stress, into a trigonal pyramid that likely serves as a precursor for the subsequent formation of a BO4 tetrahedron. PMID:25170146
NASA Astrophysics Data System (ADS)
Avetisyan, Siranush; Chakraborty, Tapash; Pietiläinen, Pekka
2016-07-01
Magnetization of anisotropic quantum dots in the presence of the Rashba spin-orbit interaction has been studied for three and four interacting electrons in the dot for non-zero values of the applied magnetic field. We observe unique behaviors of magnetization that are direct reflections of the anisotropy and the spin-orbit interaction parameters independently or concurrently. In particular, there are saw-tooth structures in the magnetic field dependence of the magnetization, as caused by the electron-electron interaction, that are strongly modified in the presence of large anisotropy and high strength of the spin-orbit interactions. We also report the temperature dependence of magnetization that indicates the temperature beyond which these structures due to the interactions disappear. Additionally, we found the emergence of a weak sawtooth structure in magnetization for three electrons in the high anisotropy and large spin-orbit interaction limit that was explained as a result of merging of two low-energy curves when the level spacings evolve with increasing values of the anisotropy and the spin-orbit interaction strength.
Bose glass and Mott glass of quasiparticles in a doped quantum magnet.
Yu, Rong; Yin, Liang; Sullivan, Neil S; Xia, J S; Huan, Chao; Paduan-Filho, Armando; Oliveira, Nei F; Haas, Stephan; Steppke, Alexander; Miclea, Corneliu F; Weickert, Franziska; Movshovich, Roman; Mun, Eun-Deok; Scott, Brian L; Zapf, Vivien S; Roscilde, Tommaso
2012-09-20
The low-temperature states of bosonic fluids exhibit fundamental quantum effects at the macroscopic scale: the best-known examples are Bose-Einstein condensation and superfluidity, which have been tested experimentally in a variety of different systems. When bosons interact, disorder can destroy condensation, leading to a 'Bose glass'. This phase has been very elusive in experiments owing to the absence of any broken symmetry and to the simultaneous absence of a finite energy gap in the spectrum. Here we report the observation of a Bose glass of field-induced magnetic quasiparticles in a doped quantum magnet (bromine-doped dichloro-tetrakis-thiourea-nickel, DTN). The physics of DTN in a magnetic field is equivalent to that of a lattice gas of bosons in the grand canonical ensemble; bromine doping introduces disorder into the hopping and interaction strength of the bosons, leading to their localization into a Bose glass down to zero field, where it becomes an incompressible Mott glass. The transition from the Bose glass (corresponding to a gapless spin liquid) to the Bose-Einstein condensate (corresponding to a magnetically ordered phase) is marked by a universal exponent that governs the scaling of the critical temperature with the applied field, in excellent agreement with theoretical predictions. Our study represents a quantitative experimental account of the universal features of disordered bosons in the grand canonical ensemble.
Takeda, Keiji; Mori, Hatsumi; Yamaguchi, Akira; Ishimoto, Hidehiko; Nakamura, Takayoshi; Kuriki, Shinya; Hozumi, Toshiya; Ohkoshi, Shin-ichi
2008-03-15
We have developed a high temperature superconductor (HTS) micrometer-sized dc superconducting quantum interference device (SQUID) magnetometer for high field and high temperature operation. It was fabricated from YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} of 92 nm in thickness with photolithography techniques to have a hole of 4x9 {mu}m{sup 2} and 2 {mu}m wide grain boundary Josephson junctions. Combined with a three dimensional magnetic field coil system, the modulation patterns of critical current I{sub c} were observed for three different field directions. They were successfully used to measure the magnetic properties of a molecular ferrimagnetic microcrystal (23x17x13 {mu}m{sup 3}), [Mn{sub 2}(H{sub 2}O){sub 2}(CH{sub 3}COO)][W(CN){sub 8}]{center_dot}2H{sub 2}O. The magnetization curve was obtained in magnetic field up to 0.12 T between 30 and 70 K. This is the first to measure the anisotropy of hysteresis curve in the field above 0.1 T with an accuracy of 10{sup -12} J T{sup -1} (10{sup -9} emu) with a HTS micro-SQUID magnetometer.
Magnon-induced long-range correlations and their neutron-scattering signature in quantum magnets
NASA Astrophysics Data System (ADS)
Bharadwaj, S.; Belitz, D.; Kirkpatrick, T. R.
2016-10-01
We consider the coupling of the magnetic Goldstone modes, or magnons, in both quantum ferromagnets and antiferromagnets to the longitudinal order-parameter fluctuations and the resulting nonanalytic behavior of the longitudinal susceptibility. In classical magnets it is well known that long-range correlations induced by the magnons lead to a singular wave-number dependence of the form 1 /k4 -d in all dimensions 2
Zeeman effect and magnetic anomalies in narrow-gap semiconductor quantum dots
NASA Astrophysics Data System (ADS)
Prado, S. J.; Trallero-Giner, C.; López-Richard, V.; Alcalde, A. M.; Marques, G. E.
2004-01-01
We present a systematic theoretical study, based on the Kane-Weiler 8×8 k· p model, of the linear Zeeman splitting introduced by the interaction between the angular momentum and the magnetic field which can give a measure of the non-linear Zeeman effect associated with interband coupling and diamagnetic contributions. The conduction and valence bands g-factors are calculated for InSb spherical and semi-spherical quantum dots. The calculations of the g-factors showed an almost linear dependence, for the ground state, on the magnetic field. We have also found that the strong magnetic field dependence as well as the dependence on the dot size of the effective spin splitting can be unambiguously attributed to the strength of the inter-level mixing.
Magnetic field control of the intraband optical absorption in two-dimensional quantum rings
NASA Astrophysics Data System (ADS)
Olendski, O.; Barakat, T.
2014-02-01
Linear and nonlinear optical absorption coefficients of the two-dimensional semiconductor ring in the perpendicular magnetic field B are calculated within independent electron approximation. Characteristic feature of the energy spectrum are crossings of the levels with adjacent nonpositive magnetic quantum numbers as the intensity B changes. It is shown that the absorption coefficient of the associated optical transition is drastically decreased at the fields corresponding to the crossing. Proposed model of the Volcano disc allows to get simple mathematical analytical results, which provide clear physical interpretation. An interplay between positive linear and intensity-dependent negative cubic absorption coefficients is discussed; in particular, critical light intensity at which additional resonances appear in the total absorption dependence on the light frequency is calculated as a function of the magnetic field and levels' broadening.
Evidence for proximity of YFe2Si2 to a magnetic quantum critical point
NASA Astrophysics Data System (ADS)
Singh, David J.
2016-06-01
Calculations of the electronic and magnetic properties of the nonmagnetic metallic compound YFe2Si2 are reported. These predict at the density functional level a magnetic state involving ordering along the c axis. This predicted ground state contrasts with experiment, which does not show magnetic order. The electronic structure is three dimensional, and is similar to that of the unconventional superconductor YFe2Ge2 as well as that of the high-pressure collapsed tetragonal phase of KFe2As2 , which is also a superconductor. Based on the results in relation to experiment, we infer that properties of YFe2Si2 are strongly influenced by a nearby antiferromagnetic quantum critical point.
Competition between applied and exchange magnetic fields in (Zn,Mn)Se/ZnTe quantum dots
NASA Astrophysics Data System (ADS)
Barman, Biplob; Tsai, Y.; Scrace, T.; Zutic, I.; McCombe, B. D.; Petrou, A.; Chou, W.-C.; Tsou, M.-H.; Yang, C.-S.; Sellers, I. R.; Oszwaldowski, R.; SUNY Buffalo Collaboration; National Chiao Tung University, Taiwan Collaboration; Graduate Institute of Electro-Optical Engineering, Tatung University, Taiwan Collaboration; University of Oklahoma Collaboration; South Dakota School of Mines; Technology Collaboration
2015-03-01
We have measured the peak energy of the photoluminescence (PL) emission and its circular polarization from type II (Zn,Mn)Se/ZnTe Quantum Dot structures in the Faraday and Voigt geometries. In the Faraday geometry the PL energy shows a 6 meV red shift at B =6 tesla. This result verifies that the holes are confined in the non-magnetic ZnTe QDs, while the electrons move in the magnetic (Zn,Mn)Se matrix. The PL circular polarization saturates at 45%. In the Voigt geometry, the circular polarization is near-zero and the red shift is 2 meV. These results are discussed using a model that takes into account that electrons are influenced by the combination of the externally applied magnetic field and the exchange field due to the interaction between the Mn-spins and the carriers. This work is supported by DOE-BES and NSF-DMR.
Engineering quantum magnetism in one-dimensional trapped Fermi gases with p -wave interactions
NASA Astrophysics Data System (ADS)
Yang, Lijun; Guan, Xiwen; Cui, Xiaoling
2016-05-01
The highly controllable ultracold atoms in a one-dimensional (1D) trap provide a new platform for the ultimate simulation of quantum magnetism. In this regard, the Néel antiferromagnetism and the itinerant ferromagnetism are of central importance and great interest. Here we show that these magnetic orders can be achieved in the strongly interacting spin-1/2 trapped Fermi gases with additional p -wave interactions. In this strong-coupling limit, the 1D trapped Fermi gas exhibits an effective Heisenberg spin X X Z chain in the anisotropic p -wave scattering channels. For a particular p -wave attraction or repulsion within the same species of fermionic atoms, the system displays ferromagnetic domains with full spin segregation or the antiferromagnetic spin configuration in the ground state. Such engineered magnetisms are likely to be probed in a quasi-1D trapped Fermi gas of 40K atoms with very close s -wave and p -wave Feshbach resonances.
Vinante, A. Falferi, P.; Mezzena, R.
2014-10-15
Superconducting Quantum Interference Device (SQUID) microsusceptometers have been widely used to study magnetic properties of materials at microscale. As intrinsically balanced devices, they could also be exploited for direct SQUID-detection of nuclear magnetic resonance (NMR) from micron sized samples, or for SQUID readout of mechanically detected NMR from submicron sized samples. Here, we demonstrate a double balancing technique that enables achievement of very low residual imbalance of a SQUID microsusceptometer over a wide bandwidth. In particular, we can generate ac magnetic fields within the SQUID loop as large as 1 mT, for frequencies ranging from dc up to a few MHz. As an application, we demonstrate direct detection of NMR from {sup 1}H spins in a glycerol droplet placed directly on top of the 20 μm SQUID loops.
Vinante, A; Mezzena, R; Falferi, P
2014-10-01
Superconducting Quantum Interference Device (SQUID) microsusceptometers have been widely used to study magnetic properties of materials at microscale. As intrinsically balanced devices, they could also be exploited for direct SQUID-detection of nuclear magnetic resonance (NMR) from micron sized samples, or for SQUID readout of mechanically detected NMR from submicron sized samples. Here, we demonstrate a double balancing technique that enables achievement of very low residual imbalance of a SQUID microsusceptometer over a wide bandwidth. In particular, we can generate ac magnetic fields within the SQUID loop as large as 1 mT, for frequencies ranging from dc up to a few MHz. As an application, we demonstrate direct detection of NMR from (1)H spins in a glycerol droplet placed directly on top of the 20 μm SQUID loops.
Magnetic field control of the intraband optical absorption in two-dimensional quantum rings
Olendski, O.; Barakat, T.
2014-02-28
Linear and nonlinear optical absorption coefficients of the two-dimensional semiconductor ring in the perpendicular magnetic field B are calculated within independent electron approximation. Characteristic feature of the energy spectrum are crossings of the levels with adjacent nonpositive magnetic quantum numbers as the intensity B changes. It is shown that the absorption coefficient of the associated optical transition is drastically decreased at the fields corresponding to the crossing. Proposed model of the Volcano disc allows to get simple mathematical analytical results, which provide clear physical interpretation. An interplay between positive linear and intensity-dependent negative cubic absorption coefficients is discussed; in particular, critical light intensity at which additional resonances appear in the total absorption dependence on the light frequency is calculated as a function of the magnetic field and levels' broadening.
Strain and localization effects in InGaAs(N) quantum wells: Tuning the magnetic response
Lopes-Oliveira, V. Herval, L. K. S.; Orsi Gordo, V.; Cesar, D. F.; Godoy, M. P. F. de; Galvão Gobato, Y.; Henini, M.; Khatab, A.; Sadeghi, M.; Wang, S.; Schmidbauer, M.
2014-12-21
We investigated effects of localization and strain on the optical and magneto-optical properties of diluted nitrogen III–V quantum wells theoretically and experimentally. High-resolution x-ray diffraction, photoluminescence (PL), and magneto-PL measurements under high magnetic fields up to 15 T were performed at low temperatures. Bir-Pikus Hamiltonian formalism was used to study the influence of strain, confinement, and localization effects. The circularly polarized magneto-PL was interpreted considering localization aspects in the valence band ground state. An anomalous behavior of the electron-hole pair magnetic shift was observed at low magnetic fields, ascribed to the increase in the exciton reduced mass due to the negative effective mass of the valence band ground state.
Violation of Bell’s inequality in a spin 1/2 quantum magnet
Chakraborty, Tanmoy Singh, Harkirat Mitra, Chiranjib
2014-04-24
Violation of Bell’s inequality test has been established as an efficient tool to determine the presence of entanglement in quantum spin 1/2 magnets. Herein, macroscopic thermodynamic quantities, namely, magnetic susceptibility and specific heat have been employed to perform Bell’s inequality test for [NH{sub 4}CuPO{sub 4}, H{sub 2}O], a spin 1/2 antiferromagnet with nearest neighbor interactions. The mean value of the Bell operator is quantified and plotted as a function of temperature. The threshold temperature is determined above which the Bell’s inequality is not violated and a good consistency is found between the analyses done on magnetic and thermal data.
Kondo-type transport through a quantum dot under magnetic fields
Dong, Bing; Lei, X. L.
2001-06-15
In this paper, we investigate the Kondo correlation effects on linear and nonlinear transport in a quantum dot connected to reservoirs under finite magnetic fields, using the slave-boson mean field approach suggested by Kotliar and Ruckenstein [Phys. Rev. Lett. >57, 1362 (1986)]. A brief comparison between the present formulation and other slave-boson formulation is presented to justify this approach. The numerical results show that the linear conductance near electron-hole symmetry is suppressed by the application of the magnetic fields, but an anomalous enhancement is predicted in the nonsymmetry regime. The effect of external magnetic fields on the nonlinear differential conductances is discussed for the Kondo system. A significant reduction of the peak splitting is observed due to the strong Kondo correlation, which agrees well with experimental data.
Quantum tricks with femtosecond light pulses teach magnetic devices to think ultrafast
NASA Astrophysics Data System (ADS)
Perakis, I. E.; Lingos, P. C.; Wang, J.
2014-03-01
The technological demand to push the gigahertz switching speed limit of today's magnetic memory/logic devices into the terahertz (1THz=1ps-1) regime underlies the entire field of spin-electronics and integrated multi- functional devices. This challenge is met by all-optical magnetic switching based on coherent spin manipulation By analogy to femto-chemistry and photosynthetic dynamics where photo-products of chemical/biochemical re- actions can be influenced by creating suitable superpositions of molecular states, femtosecond (fs) laser-excited coherence between spin/orbital/charge states can switch magnetic orders, by "suddenly" breaking the delicate balance between competing phases of correlated materials, e.g., the colossal magneto-resistive (CMR) manganites suitable for applications. Here we discuss femtosecond (fs) all-optical switching from antiferro- to ferromagnetic ordering via establishment of a magnetization increase within ˜100 fs, while the laser field still interacts with the system. Such non-equilibrium ferromagnetic correlations arise from quantum spin-flip fluctuations corre- lated with coherent superpositions of electronic states. The development of ferromagnetic correlations during the fs laser pulse reveals an initial quantum coherent regime of magnetism, clearly distinguished from the pi- cosecond lattice-heating regime characterized by phase separation. We summarize a microscopic theory based on density matrix equations of motion for composite fermion Hubbard operators, instead of bare electrons, that take into account the strong spin and charge local correlations. Our work merges two fields, femto-magnetism in metals/band insulators and non-equilibrium phase transitions of strongly correlated electrons, where local interactions exceeding the kinetic energy produce a complex balance of competing orders.
NASA Astrophysics Data System (ADS)
Pelliccione, Matthew; Jenkins, Alec; Ovartchaiyapong, Preeti; Reetz, Christopher; Emmanouilidou, Eve; Ni, Ni; Bleszynski Jayich, Ania C.
2016-08-01
High-spatial-resolution magnetic imaging has driven important developments in fields ranging from materials science to biology. However, to uncover finer details approaching the nanoscale with greater sensitivity requires the development of a radically new sensor technology. The nitrogen-vacancy (NV) defect in diamond has emerged as a promising candidate for such a sensor on the basis of its atomic size and quantum-limited sensing capabilities. It has remained an outstanding challenge to implement the NV centre as a nanoscale scanning magnetic probe at cryogenic temperatures, however, where many solid-state systems exhibit non-trivial magnetic order. Here, we present NV magnetic imaging down to 6 K with 3 μT Hz-1/2 field sensitivity, and use the technique to image vortices in the iron pnictide superconductor BaFe2(As0.7P0.3)2 with critical temperature Tc = 30 K. The expansion of NV-based magnetic imaging to cryogenic temperatures will enable future studies of previously inaccessible nanoscale magnetism in condensed-matter systems.
Magnetic forces and stationary electron flow in a three-terminal semiconductor quantum ring.
Poniedziałek, M R; Szafran, B
2010-06-01
We study stationary electron flow through a three-terminal quantum ring and describe effects due to deflection of electron trajectories by classical magnetic forces. We demonstrate that generally at high magnetic field (B) the current is guided by magnetic forces to follow a classical path, which for B > 0 leads via the left arm of the ring to the left output terminal. The transport to the left output terminal is blocked for narrow windows of magnetic field for which the interference within the ring leads to formation of wavefunctions that are only weakly coupled to the output channel wavefunctions. These interference conditions are accompanied by injection of the current to the right arm of the ring and by appearance of sharp peaks of the transfer probability to the right output terminal. We find that these peaks at high magnetic field are attenuated by thermal widening of the transport window. We also demonstrate that the interference conditions that lead to their appearance vanish when elastic scattering within the ring is present. The clear effect of magnetic forces on the transfer probabilities disappears along with Aharonov-Bohm oscillations in a chaotic transport regime that is found for rings whose width is larger than the width of the channels.
NASA Astrophysics Data System (ADS)
Pelliccione, Matthew; Jenkins, Alec; Ovartchaiyapong, Preeti; Reetz, Christopher; Emmanouilidou, Eve; Ni, Ni; Bleszynski Jayich, Ania C.
2016-08-01
High-spatial-resolution magnetic imaging has driven important developments in fields ranging from materials science to biology. However, to uncover finer details approaching the nanoscale with greater sensitivity requires the development of a radically new sensor technology. The nitrogen–vacancy (NV) defect in diamond has emerged as a promising candidate for such a sensor on the basis of its atomic size and quantum-limited sensing capabilities. It has remained an outstanding challenge to implement the NV centre as a nanoscale scanning magnetic probe at cryogenic temperatures, however, where many solid-state systems exhibit non-trivial magnetic order. Here, we present NV magnetic imaging down to 6 K with 3 μT Hz–1/2 field sensitivity, and use the technique to image vortices in the iron pnictide superconductor BaFe2(As0.7P0.3)2 with critical temperature Tc = 30 K. The expansion of NV-based magnetic imaging to cryogenic temperatures will enable future studies of previously inaccessible nanoscale magnetism in condensed-matter systems.
Pelliccione, Matthew; Jenkins, Alec; Ovartchaiyapong, Preeti; Reetz, Christopher; Emmanouilidou, Eve; Ni, Ni; Bleszynski Jayich, Ania C
2016-08-01
High-spatial-resolution magnetic imaging has driven important developments in fields ranging from materials science to biology. However, to uncover finer details approaching the nanoscale with greater sensitivity requires the development of a radically new sensor technology. The nitrogen-vacancy (NV) defect in diamond has emerged as a promising candidate for such a sensor on the basis of its atomic size and quantum-limited sensing capabilities. It has remained an outstanding challenge to implement the NV centre as a nanoscale scanning magnetic probe at cryogenic temperatures, however, where many solid-state systems exhibit non-trivial magnetic order. Here, we present NV magnetic imaging down to 6 K with 3 μT Hz(-1/2) field sensitivity, and use the technique to image vortices in the iron pnictide superconductor BaFe2(As0.7P0.3)2 with critical temperature Tc = 30 K. The expansion of NV-based magnetic imaging to cryogenic temperatures will enable future studies of previously inaccessible nanoscale magnetism in condensed-matter systems.
Pressure-induced phase transition in CrO2.
Alptekin, Sebahaddin
2015-12-01
The ab initio constant pressure molecular dynamics technique and density functional theory with generalized gradient approximation (GGA) was used to study the pressure-induced phase transition of CrO2. The phase transition of the rutile (P42/mnm) to the orthorhombic CaCl2 (Pnnm) structure at 30 GPa was determined successfully in a constant pressure simulation. This phase transition was analyzed from total energy calculations and, from the enthalpy calculation, occurred at around 17 GPa. Structural properties such as bulk modules, lattice parameters and phase transition were compared with experimental results. The phase transition at 12 ± 3 GPa was in good agreement with experimental results, as was the phase transition from the orthorhombic CaCl2 (Pnnm) to the monoclinic (P21/c) structure also found at 35 GPa.
Radiation pressure induced difference-sideband generation beyond linearized description
NASA Astrophysics Data System (ADS)
Xiong, Hao; Fan, Yu-Wan; Yang, Xiaoxue; Wu, Ying
2016-08-01
We investigate radiation-pressure induced generation of the frequency components at the difference-sideband in an optomechanical system, which beyond the conventional linearized description of optomechanical interactions between cavity fields and the mechanical oscillation. We analytically calculate amplitudes of these signals, and identify a simple square-root law for both the upper and lower difference-sideband generation which can describe the dependence of the intensities of these signals on the pump power. Further calculation shows that difference-sideband generation can be greatly enhanced via achieving the matching conditions. The effect of difference-sideband generation, which may have potential application for manipulation of light, is especially suited for on-chip optomechanical devices, where nonlinear optomechanical interaction in the weak coupling regime is within current experimental reach.
Pressure-induced transformation plasticity of H(2)O ice.
Dunand, D C; Schuh, C; Goldsby, D L
2001-01-22
Transformation plasticity is a deformation mechanism which occurs during phase transformation of an externally stressed material. Pressure-induced transformation plasticity of ice could be relevant to the geology of the moons of the outer solar system, and has long been postulated to occur in olivine in the earth's interior. In the present work, ice specimens were subjected to isostatic pressure cycling between 0 and 300 MPa to induce reversible polymorphic transformation between ice I and II at 230 K. When a small uniaxial compressive stress was applied during cycling, the specimens exhibited a compressive strain (as large as 18.5% after a single cycle) proportional to the applied stress, in agreement with observations and theory for transformation plasticity of metals induced by polymorphic thermal cycling. PMID:11177908
From quantum oscillations to charge order in high-Tc copper oxides in high magnetic fields
NASA Astrophysics Data System (ADS)
Vignolle, Baptiste; Vignolles, David; Julien, Marc-Henri; Proust, Cyril
2013-01-01
This article constitutes an update made of numerous elements from an article by Vignolle et al. [C. R. Phys. 12 (2011) 446] published in the issue of C. R. Physique dedicated to superconductivity. By including this article to the present issue on physics in high magnetic field, we have aimed, in agreement with the editorial board of the review, offering a complete issue and also reporting on the last developments in the study of superconductors in high field. We review how experiments in very high magnetic fields over the last five years have given a new twist to the understanding of the normal state of hole-doped cuprate superconductors. The discovery of quantum oscillations in underdoped YBa2Cu3Oy and overdoped Tl2Ba2CuO6 + δ has proven the existence of a Fermi surface across the whole phase diagram, which had been a controversial issue for more than twenty years. However, the striking difference in oscillation frequency for the two compounds has revealed a very different Fermi surface topology. The observation of negative Hall and Seebeck coefficients in the underdoped materials has shown that the large hole-like Fermi surface of overdoped materials undergoes a reconstruction in the high field and low temperature limits for which quantum oscillation can be observed. This has been interpreted as evidence for a translational symmetry breaking due to some form of electronic (spin, charge, or orbital current) order. The angular dependence of the quantum oscillations has constrained the source of the Fermi-surface reconstruction to something other than a spin-density wave with moments perpendicular to the field. Finally, nuclear magnetic resonance studies have revealed that it is actually charge order, without spin order, which is induced in the copper oxide planes as soon as superconductivity is sufficiently weakened by the magnetic field. The results suggest that there is a generic competition between superconductivity and a charge-density-wave instability in high
NASA Astrophysics Data System (ADS)
Boda, Aalu; Chatterjee, Ashok
2016-09-01
The problem of a neutral hydrogenic donor (D0) centre located at the centre of a GaAs quantum dot with Gaussian confinement is studied in the presence of an external magnetic field. The ground and the first excited state energies and the corresponding binding energies are obtained as functions of the potential strength, quantum dot radius and the magnetic field using a variational method. It is suggested that the first excited state of the D0 centre is bound for sufficiently strong confinement potential. The 1 s - 2p- transition energy and the magnetic susceptibilities for the ground and the first excited states are also determined.
NASA Astrophysics Data System (ADS)
Stavrou, V. N.
2016-11-01
A theoretical description of the light polarization within asymmetric self-assembled coupled quantum dots (SACQDs) in the presence of an external magnetic field, is presented. The electron and hole wavefunctions and their energy eigenvalues have been evaluated by considering ellipsoidal shaped quantum dots (QDs). Predictions of circularly light polarization for specific polarization planes, a variety of different QD geometries and the presence of an external magnetic field are displayed and compared. The results show that for some specific polarization planes the circularly light polarization is very sensitive mainly to the size of the QDs asymmetry, the interdot distance and the external magnetic field.
NASA Astrophysics Data System (ADS)
Sapega, V. F.; Belitsky, V. I.; Ruf, T.; Fuchs, H. D.; Cardona, M.; Ploog, K.
1992-12-01
A strong increase of low-frequency Raman scattering has been observed in GaAs/AlxGa1-xAs multiple quantum wells in magnetic fields up to 14 T. The spectra, consisting of background scattering, folded acoustic phonons, and additional features, show resonant behavior with respect to the laser frequency and the strength of the magnetic field. The broad background, usually related to geminate recombination, has its origin in a continuum of Raman processes with the emission of longitudinal-acoustic phonons where crystal momentum is not conserved. Such processes can become dominant when interface fluctuations allow for resonant scattering in individual quantum wells only. Thus phonons with all possible energies contribute to the background scattering efficiency. The observed folded longitudinal-acoustic phonons are in good agreement with calculated frequencies. Additional features, detected in all samples measured, are attributed to local vibrational modes tied to the gaps at the folded Brillouin-zone center and edge. Other peculiarities observed correspond to modes localized at crossings of the folded longitudinal- and transverse-acoustic branches inside the Brillouin zone. The appearance of these local modes is attributed to fluctuations in the well and barrier thicknesses of the quantum wells.
Quantum criticality and inhomogeneous magnetic order in Fe-doped α -YbAlB4
NASA Astrophysics Data System (ADS)
MacLaughlin, D. E.; Kuga, K.; Shu, Lei; Bernal, O. O.; Ho, P.-C.; Nakatsuji, S.; Huang, K.; Ding, Z. F.; Tan, C.; Zhang, Jian
2016-06-01
The intermediate-valent polymorphs α - and β -YbAlB4 exhibit quantum criticality and other novel properties not usually associated with intermediate valence. Iron doping induces quantum criticality in α -YbAlB4 and magnetic order in both compounds. We report results of muon spin relaxation (μ SR ) experiments in α -YbAl1 -xFexB4 , x =0.014 and 0.25. For x =0.014 we find no evidence for magnetic order down to 25 mK. The dynamic muon spin relaxation rate λd exhibits a power-law temperature dependence λd∝T-a , a =0.40 (4 ) , in the temperature range 100 mK-2 K, in disagreement with predictions by theories of antiferromagnetic (AFM) or valence quantum critical behavior. For x =0.25 , where AFM order develops in the temperature range 7.5-10 K, we find coexistence of meso- or macroscopically segregated paramagnetic and AFM phases, with considerable disorder in the latter down to 2 K.
Parallel magnetic field-induced conductance fluctuations in GaAs/AlGaAs ballistic quantum dots.
NASA Astrophysics Data System (ADS)
Faniel, S.; Gustin, C.; Melinte, S.; Hackens, B.; Bayot, V.; Shayegan, M.
2004-03-01
We present magnetotransport measurements in ballistic quantum dots under a parallel magnetic field. The dots were fabricated on two different GaAs/AlGaAs quantum wells with thicknesses of 15 and and 45 nm and with one and two subbands occupied, respectively. The samples were patterned using e-beam lithography and wet etching. A Cr/Au electrostatic top gate was used in order to tune the width of the dot openings. The measurements were performed down to 300 mK with the magnetic field applied strictly parallel to the plane of the two-dimensional electron gas. For both dots, we observe universal conductance fluctuations and, in the case of the wide quantum well, a reduction of their amplitude at large magnetic field. We discuss these conductance fluctuations in terms of orbital effect(V.I. Fal'ko and T. Jungwirth, Phys Rev B 65), 081306 (2002) and magnetic subband depopulation.
NASA Astrophysics Data System (ADS)
Mejri, Youssef
2016-06-01
In this article, we study the boundary inverse problem of determining the aligned magnetic field appearing in the magnetic Schrödinger equation in a periodic quantum cylindrical waveguide, by knowledge of the Dirichlet-to-Neumann map. We prove a Hölder stability estimate with respect to the Dirichlet-to-Neumann map, by means of the geometrical optics solutions of the magnetic Schrödinger equation.
Scattering-induced quantum correlation in electronic waveguides with static magnetic impurities
NASA Astrophysics Data System (ADS)
Ghanbari-Adivi, E.; Soltani, M.; Alami, Z.; Sheikhali, M.
2016-07-01
Entanglement generation due to low-energy scattering of the transporting electrons in an electronic waveguide by a quantum dot magnetic impurity is theoretically investigated. The transverse confining potential of the waveguide is considered as a two-dimensional harmonic potential, and the interaction of the electron with the impurity is described by a zero-range pseudopotential modulated by an Ising or a Heisenberg spin interaction. Our calculation shows that the scattering process leads to creation of a considerable amount of entanglement in the state of the reflected and transmitted electrons. The situation is extended to the scattering of the electrons by two well-separated magnetic impurities localized on the nanowire axis. It is shown that the scattering process causes the magnetic impurities embedded in the nanowire to share their quantum information; subsequently, they can be entangled by spin interaction with the injected electron. The created entanglement between the impurities is calculated and discussed. It is shown that the exact three-dimensional problem can be approximated as a one-dimensional problem under certain circumstances. The approximate results are compared to exact calculations and discussed.
Thermal Quantum Discord in Pure Dzyaloshinskii—Moriya Model with Magnetic Field
NASA Astrophysics Data System (ADS)
Li, Da-Chuang; Li, Xiao-Man; Cao, Zhuo-Liang
2016-06-01
We investigate the effects of the directions of Dzyaloshinskii—Moriya (DM) interaction vector and magnetic field on the quantum discord in the pure DM model. For different directions of DM vector, we find that there are different optimal parameter components of magnetic field. Moreover, we find that the optimal parameter components rules are the same for the Hamiltonian H1 and H2. According to the rules, for a certain axial DM vector, we can get the maximal quantum discord by adjusting the direction of the external magnetic field, which is feasible under the current experimental technology. Supported by the National Natural Science Foundation of China under Grant Nos. 11204061, 11374085, 11104057, and 11204002, the Anhui Provincial Natural Science Foundation under Grant No. 1408085MA16, the Anhui Provincial Candidates for Academic and Technical Leaders Foundation under Grant No. 2015H052, the discipline top-notch talents Foundation and the Excellent Young Talents Support Plan of Anhui Provincial Universities. Ming Yang is supported by National Natural Science Foundation of China under Grant No. 11274010, the Specialized Research Fund for the Doctoral Program of Higher Education under Grant No. 20113401110002, the 211 Project of Anhui University, and the Personnel Department of Anhui Province
AC transport in p-Ge/GeSi quantum well in high magnetic fields
Drichko, I. L.; Malysh, V. A.; Smirnov, I. Yu.; Golub, L. E.; Tarasenko, S. A.; Suslov, A. V.; Mironov, O. A.; Kummer, M.; Känel, H. von
2014-08-20
The contactless surface acoustic wave technique is implemented to probe the high-frequency conductivity of a high-mobility p-Ge/GeSi quantum well structure in the regime of integer quantum Hall effect (IQHE) at temperatures 0.3–5.8 K and magnetic fields up to 18 T. It is shown that, in the IQHE regime at the minima of conductivity, holes are localized and ac conductivity is of hopping nature and can be described within the “two-site” model. The analysis of the temperature and magnetic-field-orientation dependence of the ac conductivity at odd filing factors enables us to determine the effective hole g-factor, |g{sub zz}|≈4.5. It is shown that the in-plane component of the magnetic field leads to a decrease in the g-factor as well as increase in the cyclotron mass, which is explained by orbital effects in the complex valence band of germanium.
Scattering-induced quantum correlation in electronic waveguides with static magnetic impurities
NASA Astrophysics Data System (ADS)
Ghanbari-Adivi, E.; Soltani, M.; Alami, Z.; Sheikhali, M.
2016-10-01
Entanglement generation due to low-energy scattering of the transporting electrons in an electronic waveguide by a quantum dot magnetic impurity is theoretically investigated. The transverse confining potential of the waveguide is considered as a two-dimensional harmonic potential, and the interaction of the electron with the impurity is described by a zero-range pseudopotential modulated by an Ising or a Heisenberg spin interaction. Our calculation shows that the scattering process leads to creation of a considerable amount of entanglement in the state of the reflected and transmitted electrons. The situation is extended to the scattering of the electrons by two well-separated magnetic impurities localized on the nanowire axis. It is shown that the scattering process causes the magnetic impurities embedded in the nanowire to share their quantum information; subsequently, they can be entangled by spin interaction with the injected electron. The created entanglement between the impurities is calculated and discussed. It is shown that the exact three-dimensional problem can be approximated as a one-dimensional problem under certain circumstances. The approximate results are compared to exact calculations and discussed.
The quantum magnetism of individual manganese-12-acetate molecular magnets anchored at surfaces.
Kahle, Steffen; Deng, Zhitao; Malinowski, Nikola; Tonnoir, Charlène; Forment-Aliaga, Alicia; Thontasen, Nicha; Rinke, Gordon; Le, Duy; Turkowski, Volodymyr; Rahman, Talat S; Rauschenbach, Stephan; Ternes, Markus; Kern, Klaus
2012-01-11
The high intrinsic spin and long spin relaxation time of manganese-12-acetate (Mn(12)) makes it an archetypical single molecular magnet. While these characteristics have been measured on bulk samples, questions remain whether the magnetic properties replicate themselves in surface supported isolated molecules, a prerequisite for any application. Here we demonstrate that electrospray ion beam deposition facilitates grafting of intact Mn(12) molecules on metal as well as ultrathin insulating surfaces enabling submolecular resolution imaging by scanning tunneling microscopy. Using scanning tunneling spectroscopy we detect spin excitations from the magnetic ground state of the molecule at an ultrathin boron nitride decoupling layer. Our results are supported by density functional theory based calculations and establish that individual Mn(12) molecules retain their intrinsic spin on a well chosen solid support.
Kaiju, H. Kasa, H.; Mori, S.; Misawa, T.; Abe, T.; Nishii, J.; Komine, T.
2015-05-07
We investigate the Co thickness dependence of the structural and magnetic properties of Co thin-film electrodes sandwiched between borate glasses in spin quantum cross (SQC) devices that utilize stray magnetic fields. We also calculate the Co thickness dependence of the stray field between the two edges of Co thin-film electrodes in SQC devices using micromagnetic simulation. The surface roughness of Co thin films with a thickness of less than 20 nm on borate glasses is shown to be as small as 0.18 nm, at the same scanning scale as the Co film thickness, and the squareness of the hysteresis loop is shown to be as large as 0.96–1.0. As a result of the establishment of polishing techniques for Co thin-film electrodes sandwiched between borate glasses, we successfully demonstrate the formation of smooth Co edges and the generation of stray magnetic fields from Co edges. Theoretical calculation reveals that a strong stray field beyond 6 kOe is generated when the Co thickness is greater than 10 nm at a junction gap distance of 5 nm. From these experimental and calculation results, it can be concluded that SQC devices with a Co thickness of 10–20 nm can be expected to function as spin-filter devices.
Zhang, X; Bishof, M; Bromley, S L; Kraus, C V; Safronova, M S; Zoller, P; Rey, A M; Ye, J
2014-09-19
SU(N) symmetry can emerge in a quantum system with N single-particle spin states when spin is decoupled from interparticle interactions. Taking advantage of the high measurement precision offered by an ultrastable laser, we report a spectroscopic observation of SU(N ≤ 10) symmetry in (87)Sr. By encoding the electronic orbital degree of freedom in two clock states while keeping the system open to as many as 10 nuclear spin sublevels, we probed the non-equilibrium two-orbital SU(N) magnetism via Ramsey spectroscopy of atoms confined in an array of two-dimensional optical traps; we studied the spin-orbital quantum dynamics and determined the relevant interaction parameters. This study lays the groundwork for using alkaline-earth atoms as testbeds for important orbital models. PMID:25147278
Quantum magnetic flux lines, BPS vortex zero modes, and one-loop string tension shifts
NASA Astrophysics Data System (ADS)
Alonso-Izquierdo, A.; Mateos Guilarte, J.; de la Torre Mayado, M.
2016-08-01
Spectral heat kernel/zeta function regularization procedures are employed in this paper to control the divergences arising from vacuum fluctuations of Bogomolnyi-Prasad-Sommerfield vortices in the Abelian Higgs model. Zero modes of vortex fluctuations are the source of difficulties appearing when the standard Gilkey-de Witt expansion is the tool used in the calculations of one-loop shifts of vortex masses and string tensions. A modified GdW expansion is developed to diminish the impact of the infrared divergences due to the vortex zero modes of fluctuation. With this new technique at our disposal we compute the one-loop vortex mass shifts in the planar AHM and the quantum corrections to the string tension of the magnetic flux tubes living in three dimensions. In both cases it is observed that weak repulsive forces surge between these classically noninteracting topological defects caused by vacuum quantum fluctuations.
Bains, A. S.; Gill, T. S.; Misra, A. P.; Saini, N. S.
2010-01-15
The amplitude modulation of quantum ion-acoustic waves (QIAWs) along an external magnetic field is studied in a quantum electron-positron-ion (e-p-i) magnetoplasma. Reductive perturbation technique is used to derive the three-dimensional nonlinear Schroedinger equation which governs the slow modulation of QIAW packets. Accounting for the effects of the electron to ion number density ratio (mu), the normalized ion-cyclotron frequency (omega{sub c}) as well as the ratio (H) of the 'plasmonic energy density' to the Fermi energy, new regimes for the modulational instability of QIAWs are obtained and analyzed. In contrast to one-dimensional unmagnetized e-p-i plasmas, the instability growth rate is shown to suppress with increasing mu or decreasing the values of H. The predicted results could be important for understanding the salient features of modulated QIAW packets in dense astrophysical plasmas as well as to the next generation intense laser solid density plasma experiments.
Klich, I.; Lee, S.-H.; Iida, K.
2014-01-01
When spins are arranged in a lattice of triangular motif, the phenomenon of frustration leads to numerous energetically equivalent ground states, and results in exotic states such as spin liquid and spin ice. Here we report an alternative situation: a system, classically a liquid, freezes in the clean limit into a glassy state induced by quantum fluctuations. We call such glassy state a spin jam. The case in point is a frustrated magnet, where spins are arranged in a triangular network of bipyramids. Quantum corrections break the classical degeneracy into a set of aperiodic spin configurations forming local minima in a rugged energy landscape. This is established by mapping the problem into tiling with hexagonal tiles. The number of tessellations scales with the boundary length rather than its volume, showing the absence of local zero-energy modes. Low-temperature thermodynamics is discussed to compare it with other glassy materials. PMID:24686398
Dos Santos, Leonardo H R; Lanza, Arianna; Barton, Alyssa M; Brambleby, Jamie; Blackmore, William J A; Goddard, Paul A; Xiao, Fan; Williams, Robert C; Lancaster, Tom; Pratt, Francis L; Blundell, Stephen J; Singleton, John; Manson, Jamie L; Macchi, Piero
2016-02-24
The accurate electron density distribution and magnetic properties of two metal-organic polymeric magnets, the quasi-one-dimensional (1D) Cu(pyz)(NO3)2 and the quasi-two-dimensional (2D) [Cu(pyz)2(NO3)]NO3·H2O, have been investigated by high-resolution single-crystal X-ray diffraction and density functional theory calculations on the whole periodic systems and on selected fragments. Topological analyses, based on quantum theory of atoms in molecules, enabled the characterization of possible magnetic exchange pathways and the establishment of relationships between the electron (charge and spin) densities and the exchange-coupling constants. In both compounds, the experimentally observed antiferromagnetic coupling can be quantitatively explained by the Cu-Cu superexchange pathway mediated by the pyrazine bridging ligands, via a σ-type interaction. From topological analyses of experimental charge-density data, we show for the first time that the pyrazine tilt angle does not play a role in determining the strength of the magnetic interaction. Taken in combination with molecular orbital analysis and spin density calculations, we find a synergistic relationship between spin delocalization and spin polarization mechanisms and that both determine the bulk magnetic behavior of these Cu(II)-pyz coordination polymers.
NASA Astrophysics Data System (ADS)
Çakır, Bekir; Atav, Ülfet; Yakar, Yusuf; Özmen, Ayhan
2016-08-01
In this study we report a detailed theoretical investigation of the effect of an external magnetic field on the 1s-, 2p-, 3d- and 4f-energy states of a spherical quantum dot. We treat the contribution of the diamagnetic term as a perturbation and discuss the effect of the diamagnetic term on the 1s-, 2p-, 3d- and 4f-energy states. We also have calculated the Zeeman transition energies between 2p → 1s and 3d → 2p states with m = 0, ±1 and 0, ±1, ±2 as a function of dot radius and the magnetic field strength. The results show that the magnetic field, impurity charge and dot radius have a strong influence on the energy states and the Zeeman transitions. It is found that the energies of the electronic states with m < 0 addition of the diamagnetic term firstly decrease toward a minimum, and then increase with the increasing magnetic field strength. We have seen that as magnetic field intensity is adjusted, frequency of the emitted light can be changed for Zeeman transitions.
Dos Santos, Leonardo H R; Lanza, Arianna; Barton, Alyssa M; Brambleby, Jamie; Blackmore, William J A; Goddard, Paul A; Xiao, Fan; Williams, Robert C; Lancaster, Tom; Pratt, Francis L; Blundell, Stephen J; Singleton, John; Manson, Jamie L; Macchi, Piero
2016-02-24
The accurate electron density distribution and magnetic properties of two metal-organic polymeric magnets, the quasi-one-dimensional (1D) Cu(pyz)(NO3)2 and the quasi-two-dimensional (2D) [Cu(pyz)2(NO3)]NO3·H2O, have been investigated by high-resolution single-crystal X-ray diffraction and density functional theory calculations on the whole periodic systems and on selected fragments. Topological analyses, based on quantum theory of atoms in molecules, enabled the characterization of possible magnetic exchange pathways and the establishment of relationships between the electron (charge and spin) densities and the exchange-coupling constants. In both compounds, the experimentally observed antiferromagnetic coupling can be quantitatively explained by the Cu-Cu superexchange pathway mediated by the pyrazine bridging ligands, via a σ-type interaction. From topological analyses of experimental charge-density data, we show for the first time that the pyrazine tilt angle does not play a role in determining the strength of the magnetic interaction. Taken in combination with molecular orbital analysis and spin density calculations, we find a synergistic relationship between spin delocalization and spin polarization mechanisms and that both determine the bulk magnetic behavior of these Cu(II)-pyz coordination polymers. PMID:26811927
Salim, Michael A; Willow, Soohaeng Yoo; Hirata, So
2016-05-28
Ice Ih displays several anomalous thermodynamic properties such as thermal contraction at low temperatures, an anomalous volume isotope effect (VIE) rendering the volume of D2O ice greater than that of H2O ice, and a pressure-induced transition to the high-density amorphous (HDA) phase. Furthermore, the anomalous VIE increases with temperature, despite its quantum-mechanical origin. Here, embedded-fragment ab initio second-order many-body perturbation (MP2) theory in the quasiharmonic approximation (QHA) is applied to the Gibbs energy of an infinite, proton-disordered crystal of ice Ih at wide ranges of temperatures and pressures. The quantum effect of nuclei moving in anharmonic potentials is taken into account from first principles without any empirical or nonsystematic approximation to either the electronic or vibrational Hamiltonian. MP2 predicts quantitatively correctly the thermal contraction at low temperatures, which is confirmed to originate from the volume-contracting hydrogen-bond bending modes (acoustic phonons). It qualitatively reproduces (but underestimates) the thermal expansion at higher temperatures, caused by the volume-expanding hydrogen-bond stretching (and to a lesser extent librational) modes. The anomalous VIE is found to be the result of subtle cancellations among closely competing isotope effects on volume from all modes. Consequently, even ab initio MP2 with the aug-cc-pVDZ and aug-cc-pVTZ basis sets has difficulty reproducing this anomaly, yielding qualitatively varied predictions of the sign of the VIE depending on such computational details as the choice of the embedding field. However, the temperature growth of the anomalous VIE is reproduced robustly and is ascribed to the librational modes. These solid-state MP2 calculations, as well as MP2 Born-Oppenheimer molecular dynamics, find a volume collapse and a loss of symmetry and long-range order in ice Ih upon pressure loading of 2.35 GPa or higher. Concomitantly, rapid softening of
NASA Astrophysics Data System (ADS)
Salim, Michael A.; Willow, Soohaeng Yoo; Hirata, So
2016-05-01
Ice Ih displays several anomalous thermodynamic properties such as thermal contraction at low temperatures, an anomalous volume isotope effect (VIE) rendering the volume of D2O ice greater than that of H2O ice, and a pressure-induced transition to the high-density amorphous (HDA) phase. Furthermore, the anomalous VIE increases with temperature, despite its quantum-mechanical origin. Here, embedded-fragment ab initio second-order many-body perturbation (MP2) theory in the quasiharmonic approximation (QHA) is applied to the Gibbs energy of an infinite, proton-disordered crystal of ice Ih at wide ranges of temperatures and pressures. The quantum effect of nuclei moving in anharmonic potentials is taken into account from first principles without any empirical or nonsystematic approximation to either the electronic or vibrational Hamiltonian. MP2 predicts quantitatively correctly the thermal contraction at low temperatures, which is confirmed to originate from the volume-contracting hydrogen-bond bending modes (acoustic phonons). It qualitatively reproduces (but underestimates) the thermal expansion at higher temperatures, caused by the volume-expanding hydrogen-bond stretching (and to a lesser extent librational) modes. The anomalous VIE is found to be the result of subtle cancellations among closely competing isotope effects on volume from all modes. Consequently, even ab initio MP2 with the aug-cc-pVDZ and aug-cc-pVTZ basis sets has difficulty reproducing this anomaly, yielding qualitatively varied predictions of the sign of the VIE depending on such computational details as the choice of the embedding field. However, the temperature growth of the anomalous VIE is reproduced robustly and is ascribed to the librational modes. These solid-state MP2 calculations, as well as MP2 Born-Oppenheimer molecular dynamics, find a volume collapse and a loss of symmetry and long-range order in ice Ih upon pressure loading of 2.35 GPa or higher. Concomitantly, rapid softening of
Spanget-Larsen, J. ); Waluk, J. ); Thulstrup, E.W. )
1990-03-08
The electronic transitions of chrysene are investigated by linear dichroism spectroscopy in stretched polyethylene and by magnetic circular dichroism spectroscopy, leading to the assignment of seven excited singlet states below 47,000 cm{sup {minus}1}. One of these has not previously been observed. The linear dichroism data, combined with previously published fluorescence polarization results, lead to precise determination of transition moment directions for five transitions. The experimental results are compared with theoretical predictions with the PPP, LCOAO, CNDO/S, and INDO/S quantum chemical models.
First-principles theory of quantum well resonance in double barrier magnetic tunnel junctions.
Wang, Yan; Lu, Zhong-Yi; Zhang, X-G; Han, X F
2006-08-25
Quantum well (QW) resonances in Fe(001)/MgO/Fe/MgO/Fe double barrier magnetic tunnel junctions are calculated from first principles. By including the Coulomb blockade energy due to the finite size islands of the middle Fe film, we confirm that the oscillatory differential resistance observed in a recent experiment [T. Nozaki, Phys. Rev. Lett. 96, 027208 (2006)10.1103/PhysRevLett.96.027208] originates from the QW resonances from the Delta1 band of the Fe majority-spin channel. The primary source of smearing at low temperatures is shown to be the variation of the Coulomb blockade energy.
Nonlocal magnetic configuration controlling realized in a triple-quantum-dot Josephson junction
NASA Astrophysics Data System (ADS)
Yi, Guang-Yu; Wang, Xiao-Qi; Wu, Hai-Na; Gong, Wei-Jiang
2016-07-01
We investigate the Josephson effect in a superconductor/triple-quantum-dot/superconductor junction in which the central dot is coupled to the superconductors. It is found that the supercurrent exhibits rich 0-π phase translations due to the interplay between interdot spin and electron correlations. Moreover, when the side dots are half-occupied, the nonlocal spin correlation between them, i.e., ferromagnetic or antiferromagnetic, coincides well with the supercurrent phase. We thus consider such a system to be a promising candidate for controlling the nonlocal magnetic configuration based on the Josephson effect.
Uran, Can; Erdem, Talha; Guzelturk, Burak; Perkgöz, Nihan Kosku; Jun, Shinae; Jang, Eunjoo; Demir, Hilmi Volkan
2014-10-06
In this work, we demonstrate a proof-of-concept system for generating highly polarized light from colloidal quantum dots (QDs) coupled with magnetically aligned segmented Au/Ni/Au nanowires (NWs). Optical characterizations reveal that the optimized QD-NW coupled structures emit highly polarized light with an s-to p-polarization (s/p) contrast as high as 15:1 corresponding to a degree of polarization of 0.88. These experimental results are supported by the finite-difference time-domain simulations, which demonstrate the interplay between the inter-NW distance and the degree of polarization.
Light and electric field control of ferromagnetism in magnetic quantum structures.
Boukari, H; Kossacki, P; Bertolini, M; Ferrand, D; Cibert, J; Tatarenko, S; Wasiela, A; Gaj, J A; Dietl, T
2002-05-20
A strong influence of illumination and electric bias on the Curie temperature and saturation value of the magnetization is demonstrated for semiconductor structures containing a modulation-doped p-type Cd(0.96)Mn(0.04)Te quantum well placed in various built-in electric fields. It is shown that both light beam and bias voltage generate an isothermal and reversible crossover between the paramagnetic and ferromagnetic phases, in the way that is predetermined by the structure design. The observed behavior is in quantitative agreement with the expectations for systems, in which ferromagnetic interactions are mediated by the weakly disordered two-dimensional hole liquid.
Weakly relativistic quantum kinetic theory for electrostatic wave modes in magnetized plasmas
Hussain, Azhar; Stefan, Martin; Brodin, Gert
2014-03-15
We have derived the electrostatic dispersion relation in a magnetized plasma using a recently developed quantum kinetic model based on the Dirac equation. The model contains weakly relativistic spin effects such as Thomas precession, the polarization currents associated with the spin and the spin-orbit coupling. It turns out that for strictly electrostatic perturbations the non-relativistic spin effects vanish, and the modification of the classical dispersion relation is solely associated with the relativistic terms. Several new wave modes appear due the electron spin effects, and an example for astrophysical plasmas are given.
Insulator, semiclassical oscillations and quantum Hall liquids at low magnetic fields.
Lo, Shun-Tsung; Wang, Yi-Ting; Bohra, G; Comfort, E; Lin, T-Y; Kang, M-G; Strasser, G; Bird, J P; Huang, C F; Lin, Li-Hung; Chen, J C; Liang, C-T
2012-10-10
Magneto-transport measurements are performed on two-dimensional GaAs electron systems to probe the quantum Hall (QH) effect at low magnetic fields. Oscillations following the Shubnikov-de Haas (SdH) formula are observed in the transition from the insulator to QH liquid when the observed almost temperature-independent Hall slope indicates insignificant interaction correction. Our study shows that the existence of SdH oscillations in such a transition can be understood based on the non-interacting model.
NASA Astrophysics Data System (ADS)
Dubey, Sudipta; Deshmukh, Mandar M.
2016-07-01
We probe quantum Hall effect in a tunable 1-D lateral superlattice (SL) in graphene created using electrostatic gates. Lack of equilibration is observed along edge states formed by electrostatic gates inside the superlattice. We create strong local electric field at the interface of regions of different charge densities. Crossed electric and magnetic fields modify the wavefunction of the Landau Levels (LLs) - a phenomenon unique to graphene. In the region of copropagating electrons and holes at the interface, the electric field is high enough to modify the Landau levels resulting in increased scattering that tunes equilibration of edge states and this results in large longitudinal resistance.
Zhang, Hao; Zhang, Guang-Ming; Yu, Lu
2009-04-15
A correct general formula for the spin current through an interacting quantum dot coupled to ferromagnetic leads with magnetization at an arbitrary angle θ is derived within the framework of the Keldysh formalism. Under asymmetric conditions, the spin current component J(z) may change sign for 0<θ<π. It is shown that the spin current and spin tunneling magnetoresistance exhibit different angle dependence in the free and Coulomb blockade regimes. In the latter case, the competition of the spin precession and the spin-valve effect could lead to an anomaly in the angle dependence of the spin current. PMID:21825366
Quantum ring conductance sensitivity to potential perturbation in an external magnetic field
NASA Astrophysics Data System (ADS)
Chwiej, T.; Szafran, B.
2014-05-01
We study the sensitivity of quantum ring (QR) conductance to potential perturbation introduced by an external charged probe in the context of scanning gate microscopy experiments and analyze its correspondence to the local density of states at the Fermi level for up to four subbands participating in the transport. We find that the conductance of the QR can be weakly sensitive or almost insensitive to the perturbation potential due to magnetic deflection of the wave function. The conductance becomes very sensitive to external perturbations at localized resonances for which the local density of states can be extracted by conductance mapping.
Quantum paraelectricity in copper-titanates: Magnetic-order driven vitrification
Kumar, Jitender; Awasthi, A. M.
2015-07-21
Quantum-paraelectric (QP) family character is emergent from shared low-temperature characteristics of SrCu{sub 3}Ti{sub 4}O{sub 12} (SCTO), CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO), and Ca{sub 0.9}Li{sub 0.1}Cu{sub 3}Ti{sub 4}O{sub 12} (CLCTO) A{sub 1/4}A′{sub 3/4}BO{sub 3} structures featuring antiferro-tilted Ti-O{sub 6} octahedra. Above their magnetic ordering temperatures T{sub N}, permittivity of SCTO and CLCTO follow typical Barrett form, whereas in CCTO, quantum paraelectricity is masked by the huge ε′-step. Hidden QP in CCTO gets revealed by Li-doping at the Ca-site, which considerably up-shifts the temperature scale (from ∼100 K to ∼250 K) of the dielectric step-anomaly in CLCTO. Competing magneto-electricity and quantum fluctuations result in glassy-arrest of the QP degrees of freedom near T{sub N}; manifest as dispersive-deviation of the permittivity (in SCTO and CLCTO) from the low-temperature Barrett saturation. However, quantum criticality (QC) regime being well above T{sub N} registers its presence nevertheless, as the ∼T{sup 2} behaviour of their inverse dielectric susceptibility. Non-compliance to the usual behaviours of dispersive-response vs. bias-field and temperature unambiguously rule out a relaxor origin of the glassy state. We determine a dimensionless thermal window (0.3 ≤ T/T{sub 1} ≤ 0.6) of QC signature, covering typical quantum-paraelectrics.
NASA Astrophysics Data System (ADS)
Dehyar, A.; Rezaei, G.; Zamani, A.
2016-10-01
In the present work, we have investigated the simultaneous effects of external electric and magnetic fields on the energy spectrum of an electron bound to an impurity confined in a spherical quantum dot with Kratzer potential. To this end, energy eigenvalues are obtained using the asymptotic iteration method. The energy dependencies upon the confinement potential and external fields are reported. Our results indicate that the confinement potential, external electric and magnetic fields have a great influence on the energy eigenvalues of the system. We found that, an increase in the magnetic field increases the energy eigenvalues of the states with positive magnetic quantum number, m ≽ 0 . While, the states with negative m decrease, reaching to their minimum values and increase again, with increasing the magnetic field. Moreover, an increase in electric field strength leads to decrease the confinement effects and energy eigenvalues of the system.
Kushwaha, Manvir S.
2014-12-15
Semiconducting quantum dots – more fancifully dubbed artificial atoms – are quasi-zero dimensional, tiny, man-made systems with charge carriers completely confined in all three dimensions. The scientific quest behind the synthesis of quantum dots is to create and control future electronic and optical nanostructures engineered through tailoring size, shape, and composition. The complete confinement – or the lack of any degree of freedom for the electrons (and/or holes) – in quantum dots limits the exploration of spatially localized elementary excitations such as plasmons to direct rather than reciprocal space. Here we embark on a thorough investigation of the magneto-optical absorption in semiconducting spherical quantum dots characterized by a confining harmonic potential and an applied magnetic field in the symmetric gauge. This is done within the framework of Bohm-Pines’ random-phase approximation that enables us to derive and discuss the full Dyson equation that takes proper account of the Coulomb interactions. As an application of our theoretical strategy, we compute various single-particle and many-particle phenomena such as the Fock-Darwin spectrum; Fermi energy; magneto-optical transitions; probability distribution; and the magneto-optical absorption in the quantum dots. It is observed that the role of an applied magnetic field on the absorption spectrum is comparable to that of a confining potential. Increasing (decreasing) the strength of the magnetic field or the confining potential is found to be analogous to shrinking (expanding) the size of the quantum dots: resulting into a blue (red) shift in the absorption spectrum. The Fermi energy diminishes with both increasing magnetic-field and dot-size; and exhibits saw-tooth-like oscillations at large values of field or dot-size. Unlike laterally confined quantum dots, both (upper and lower) magneto-optical transitions survive even in the extreme instances. However, the intra-Landau level
Eom, Byeong Ho; Penanen, Konstantin; Hahn, Inseob
2014-09-15
Magnetic resonance imaging (MRI) at microtesla fields using superconducting quantum interference device (SQUID) detection has previously been demonstrated, and advantages have been noted. Although the ultralow-field SQUID MRI technique would not need the heavy superconducting magnet of conventional MRI systems, liquid helium required to cool the low-temperature detector still places a significant burden on its operation. We have built a prototype cryocooler-based SQUID MRI system that does not require a cryogen. The SQUID detector and the superconducting gradiometer were cooled down to 3.7 K and 4.3 K, respectively. We describe the prototype design, characterization, a phantom image, and areas of further improvements needed to bring the imaging performance to parity with conventional MRI systems.
NASA Astrophysics Data System (ADS)
Pavlović, Vladan; Stevanović, Ljiljana
2016-04-01
In this paper we analyzed the realization of the electromagnetically induced transparency (EIT) effect in the spherical quantum dot with on-center hydrogenic impurity under the influence of the external magnetic field. Three energy levels of hydrogen impurity 1s0, 2p-1, and 3d-2, together with the probe and control laser fields, which induce σ- transitions between the given states, form a ladder configuration. Optical Bloch equations for such a system are solved in a stationary regime. Dependence of the susceptibility for such a system on the Rabi frequency of the control field, intensity of the external magnetic field, detuning of the control field, and decay rates coefficients are then discussed in detail. Finally, the explanation in dressed state picture is given.
Eom, Byeong Ho; Penanen, Konstantin; Hahn, Inseob
2014-09-01
Magnetic resonance imaging (MRI) at microtesla fields using superconducting quantum interference device (SQUID) detection has previously been demonstrated, and advantages have been noted. Although the ultralow-field SQUID MRI technique would not need the heavy superconducting magnet of conventional MRI systems, liquid helium required to cool the low-temperature detector still places a significant burden on its operation. We have built a prototype cryocooler-based SQUID MRI system that does not require a cryogen. The SQUID detector and the superconducting gradiometer were cooled down to 3.7 K and 4.3 K, respectively. We describe the prototype design, characterization, a phantom image, and areas of further improvements needed to bring the imaging performance to parity with conventional MRI systems. PMID:25273745
Eom, Byeong Ho; Penanen, Konstantin; Hahn, Inseob
2014-09-01
Magnetic resonance imaging (MRI) at microtesla fields using superconducting quantum interference device (SQUID) detection has previously been demonstrated, and advantages have been noted. Although the ultralow-field SQUID MRI technique would not need the heavy superconducting magnet of conventional MRI systems, liquid helium required to cool the low-temperature detector still places a significant burden on its operation. We have built a prototype cryocooler-based SQUID MRI system that does not require a cryogen. The SQUID detector and the superconducting gradiometer were cooled down to 3.7 K and 4.3 K, respectively. We describe the prototype design, characterization, a phantom image, and areas of further improvements needed to bring the imaging performance to parity with conventional MRI systems.
NASA Astrophysics Data System (ADS)
Eom, Byeong Ho; Penanen, Konstantin; Hahn, Inseob
2014-09-01
Magnetic resonance imaging (MRI) at microtesla fields using superconducting quantum interference device (SQUID) detection has previously been demonstrated, and advantages have been noted. Although the ultralow-field SQUID MRI technique would not need the heavy superconducting magnet of conventional MRI systems, liquid helium required to cool the low-temperature detector still places a significant burden on its operation. We have built a prototype cryocooler-based SQUID MRI system that does not require a cryogen. The SQUID detector and the superconducting gradiometer were cooled down to 3.7 K and 4.3 K, respectively. We describe the prototype design, characterization, a phantom image, and areas of further improvements needed to bring the imaging performance to parity with conventional MRI systems.
NASA Astrophysics Data System (ADS)
Chwiej, T.
2016-10-01
We theoretically study the single electron magnetotransport in GaAs and InGaAs vertically stacked bilayer nanowires. In considered geometry, the tilted magnetic field is always perpendicular to the main (transport) axis of the quantum wire and, therefore its transverse and vertical components allow separately for changing the magnitude of intralayer and interlayer subbands mixing. We study the changes introduced to energy dispersion relation E(k) by tilted magnetic field of strength up to several tesla and analyze their origins for symmetric as well as asymmetric confining potentials in the growth direction. Calculated energy dispersion relations are thereafter used to show that the value of a conductance of the bilayer nanowire may abruptly rise as well as fall by few conductance quanta when the Fermi energy in nanosystem is changed. It is also shown that such conductance oscillations, in conjunction with spin Zeeman effect, may give a moderately spin polarized current in the bilayer nanowire.
van Schooten, Kipp J; Boehme, Christoph; Lupton, John M
2014-06-23
Blinking of colloidal nanocrystal quantum dots, random intermittency in the stream of photons emitted by single particles, has long commanded the curiosity of researchers. Why does the particle suddenly shut off, and what are the pathways to quench emission? Single-particle microscopy is not the only way to approach these fundamental questions on the interaction of light and matter: time-domain sub-ensemble spectroscopies can also yield relevant information on microscopic electronic processes. We illustrate recent advances in pulsed optically detected magnetic resonance and highlight the conceptual relevance to unravelling mechanisms controlling intermittency on the single-particle level. Magnetic resonance reveals two distinct luminescence quenching channels, which appear to be related to those previously surmised from single-particle studies: a trapped charge-separated state in which the exciton is quenched by dissociation and the particle remains neutral; and a charged state of the particle in which spin-dependent Auger recombination quenches luminescence.
Lasing and magnetic microbeads loaded with colloidal quantum dots and iron oxide nanocrystals
NASA Astrophysics Data System (ADS)
Li, Minxu; You, Guanjun; Wang, Andrew Y.; Hu, Wenjia; Wang, Jingkang; Sun, Fengqing; Zhu, Yiming; Henderson, Ron; Xu, Jian
2013-09-01
This study investigates the feasibility of loading nanostructured lasing medium and magnetic nanocrystals in the same microbead for potential applications in bio- and chemical sensing. A sequential infiltration process is proposed and tested for the preparation of magnetic and lasing microbeads by incorporating, respectively, iron oxide nanocrystals in the inner cores and colloidal quantum dots (CQDs) in the periphery regions of mesoporous silica microbeads. The co-doped bead structure was confirmed by electron microscopy and energy dispersive spectroscopy. The lasing action of the CQD gain medium in the mesoporous beads was characterized with micro-photoluminescence, revealing sharp whispering gallery mode lasing signatures, whereas the distinguishing superparamagnetic property was measured from the co-doped microbeads with vibrating sample magnetometry.
On the quantum magnetic oscillations of electrical and thermal conductivities of graphene
NASA Astrophysics Data System (ADS)
Alisultanov, Z. Z.; Reis, M. S.
2016-05-01
Oscillating thermodynamic quantities of diamagnetic materials, specially graphene, have been attracting attention of the scientific community due to the possibility to experimentally map the Fermi surface of the material. These have been the case of the de Haas-van Alphen and Shubnikov-de Haas effects, found on the magnetization and electrical conductivity, respectively. In this direction, managing the thermodynamic oscillations is of practical purpose, since from the reconstructed Fermi surface it is possible to access, for instance, the electronic density. The present work theoretically explores the quantum oscillations of electrical and thermal conductivities of a monolayer graphene under a crossed magnetic and electric fields. We found that the longitudinal electric field can increase the amplitude of the oscillations and this result is of practical and broad interest for both, experimental and device physics.
Quantum anomalous Hall effect in atomic crystal layers from in-plane magnetization
NASA Astrophysics Data System (ADS)
Ren, Yafei; Zeng, Junjie; Deng, Xinzhou; Yang, Fei; Pan, Hui; Qiao, Zhenhua
2016-08-01
We theoretically demonstrate that with in-plane magnetization, the quantum anomalous Hall effect (QAHE) can be realized in two-dimensional atomic crystal layers with preserved inversion symmetry but broken out-of-plane mirror reflection symmetry. By taking the honeycomb lattice system as an example, we find that the low-buckled structure satisfying the symmetry criteria is crucial to induce QAHE. The topologically nontrivial bulk gap carrying a Chern number of C =±1 opens in the vicinity of the saddle points M , where the band dispersion exhibits strong anisotropy. We further show that the QAHE with electrically tunable Chern number can be achieved in Bernal-stacked multilayer systems, and the applied interlayer potential differences can dramatically decrease the critical magnetization to make the QAHE experimentally feasible.
Shot noise of charge current in a quantum dot responded by rotating and oscillating magnetic fields
Zhao, Hong-Kang Zou, Wei-Ke; Chen, Qiao
2014-09-07
We have investigated the shot noise and Fano factor of the dynamic spin-polarized quantum dot under the perturbations of a rotating magnetic field (RMF), and an oscillating magnetic field (OMF) by employing the non-equilibrium Green's function approach. The shot noise is enhanced from sub-Poissonian to super-Poissonian due to the application of RMF and OMF, and it is controlled sensitively by the tilt angle θ of RMF. The magnitude of shot noise increases as the photon energy ℏω of OMF increases, and its valley eventually is reversed to peaks as the photon energy is large enough. Double-peak structure of Fano factor is exhibited as the frequency of OMF increases to cover a large regime. The Zeeman energy μ{sub 0}B{sub 0} acts as an effective gate bias to exhibit resonant behavior, and novel peak emerges associated with the applied OMF.
Quantization and Excitation of Longitudinal Electrostatic Waves in Magnetized Quantum Plasmas
NASA Astrophysics Data System (ADS)
Tsintsadze, Levan N.
2010-12-01
Effects of the Landau diamagnetism and the Pauli paramagnetism on the longitudinal electric wave characteristics in a quantum plasma are studied. It is shown that a dispersion relation of the longitudinal wave propagating along a magnetic field strongly depends on the magnetic field, in radical contrast to the classical case. Instabilities of the quantized longitudinal electric waves are studied by a newly derived dispersion equation. Novel branches of longitudinal waves are found, which have no analogies without the Landau quantization. Growth rates of these new modes are obtained. The excitation of the zero sound by an electron beam is discussed and found that the quantization of the energy of electrons imposes a new condition. Furthermore, the excitation of Bogolyubov's type of spectrum by a strong electric field is considered.
NASA Astrophysics Data System (ADS)
Zamar, R. C.; Mensio, O.
2004-12-01
By means of the Jeener-Broekaert nuclear magnetic resonance pulse sequence, the proton spin system of a liquid crystal can be prepared in quasiequilibrium states of high dipolar order, which relax to thermal equilibrium with the molecular environment with a characteristic time (T1D). Previous studies of the Larmor frequency and temperature dependence of T1D in thermotropic liquid crystals, that included field cycling and conventional high-field experiments, showed that the slow hydrodynamic modes dominate the behavior of T1D, even at high Larmor frequencies. This noticeable predominance of the cooperative fluctuations (known as order fluctuations of the director, OFD) could not be explained by standard models based on the spin-lattice relaxation theory in the limit of high temperature (weak order). This fact points out the necessity of investigating the role of the quantum terms neglected in the usual high temperature theory of dipolar order relaxation. In this work, we present a generalization of the proton dipolar order relaxation theory for highly correlated systems, which considers all the spins belonging to correlated domains as an open quantum system interacting with quantum bath. As starting point, we deduce a formulation of the Markovian master equation of relaxation for the statistical spin operator, valid for all temperatures, which is suitable for introducing a dipolar spin temperature in the quantum regime, without further assumptions about the form of the spin-lattice Hamiltonian. In order to reflect the slow dynamics occurring in correlated systems, we lift the usual short-correlation-time assumption by including the average over the motion of the dipolar Hamiltonian together with the Zeeman Hamiltonian into the time evolution operator. In this way, we calculate the time dependence of the spin operators in the interaction picture in a closed form, valid for high magnetic fields, bringing into play the spin-spin interactions within the microscopic time
NASA Astrophysics Data System (ADS)
Taufour, Valentin; Kaluarachchi, Udhara S.; Khasanov, Rustem; Nguyen, Manh Cuong; Guguchia, Zurab; Biswas, Pabitra Kumar; Bonfà, Pietro; De Renzi, Roberto; Lin, Xiao; Kim, Stella K.; Mun, Eun Deok; Kim, Hyunsoo; Furukawa, Yuji; Wang, Cai-Zhuang; Ho, Kai-Ming; Bud'ko, Sergey L.; Canfield, Paul C.
2016-07-01
The temperature-pressure phase diagram of the ferromagnet LaCrGe3 is determined for the first time from a combination of magnetization, muon-spin-rotation, and electrical resistivity measurements. The ferromagnetic phase is suppressed near 2.1 GPa, but quantum criticality is avoided by the appearance of a magnetic phase, likely modulated, AFMQ . Our density functional theory total energy calculations suggest a near degeneracy of antiferromagnetic states with small magnetic wave vectors Q allowing for the potential of an ordering wave vector evolving from Q =0 to finite Q , as expected from the most recent theories on ferromagnetic quantum criticality. Our findings show that LaCrGe3 is a very simple example to study this scenario of avoided ferromagnetic quantum criticality and will inspire further study on this material and other itinerant ferromagnets.
NASA Astrophysics Data System (ADS)
Gumber, Sukirti; Gambhir, Monica; Jha, Pradip Kumar; Mohan, Man
2016-10-01
We study the combined effect of hydrostatic pressure and magnetic field on electromagnetically induced transparency in quantum ring. The high flexibility in size and shape of ring makes it possible to fabricate a nearly perfect two-dimensional quantum structure. We also explore the dependence of frequency conversion, measured in terms of third order nonlinear susceptibility χ(3) , on coupling field, hydrostatic pressure and magnetic field. Although, a dip in χ(3) is observed with the introduction of strong coupling field, it renders the ring structure transparent to generated wave thus effectively enhancing the output of nonlinear frequency conversion process. At a fixed coupling strength, the output can be further enhanced by increasing the magnetic field while it shows an inverse relationship with pressure. These parameters, being externally controlled, provide an easy handle to control the output of quantum ring which can be used as frequency converter in communication networks.
Taufour, Valentin; Kaluarachchi, Udhara S; Khasanov, Rustem; Nguyen, Manh Cuong; Guguchia, Zurab; Biswas, Pabitra Kumar; Bonfà, Pietro; De Renzi, Roberto; Lin, Xiao; Kim, Stella K; Mun, Eun Deok; Kim, Hyunsoo; Furukawa, Yuji; Wang, Cai-Zhuang; Ho, Kai-Ming; Bud'ko, Sergey L; Canfield, Paul C
2016-07-15
The temperature-pressure phase diagram of the ferromagnet LaCrGe_{3} is determined for the first time from a combination of magnetization, muon-spin-rotation, and electrical resistivity measurements. The ferromagnetic phase is suppressed near 2.1 GPa, but quantum criticality is avoided by the appearance of a magnetic phase, likely modulated, AFM_{Q}. Our density functional theory total energy calculations suggest a near degeneracy of antiferromagnetic states with small magnetic wave vectors Q allowing for the potential of an ordering wave vector evolving from Q=0 to finite Q, as expected from the most recent theories on ferromagnetic quantum criticality. Our findings show that LaCrGe_{3} is a very simple example to study this scenario of avoided ferromagnetic quantum criticality and will inspire further study on this material and other itinerant ferromagnets. PMID:27472137
Taufour, Valentin; Kaluarachchi, Udhara S.; Khasanov, Rustem; Nguyen, Manh Cuong; Guguchia, Zurab; Biswas, Pabitra Kumar; Bonfa, Pietro; De Renzi, Roberto; Lin, Xiao; Kim, Stella K.; et al
2016-07-13
Here, the temperature-pressure phase diagram of the ferromagnet LaCrGe3 is determined for the first time from a combination of magnetization, muon-spin-rotation, and electrical resistivity measurements. The ferromagnetic phase is suppressed near 2.1 GPa, but quantum criticality is avoided by the appearance of a magnetic phase, likely modulated, AFMQ. Our density functional theory total energy calculations suggest a near degeneracy of antiferromagnetic states with small magnetic wave vectors Q allowing for the potential of an ordering wave vector evolving from Q=0 to finite Q, as expected from the most recent theories on ferromagnetic quantum criticality. Our findings show that LaCrGe3 ismore » a very simple example to study this scenario of avoided ferromagnetic quantum criticality and will inspire further study on this material and other itinerant ferromagnets.« less
Effect of disorder on the pressure-induced superconducting state of CeAu 2Si 2
NASA Astrophysics Data System (ADS)
Ren, Z.; Giriat, G.; Scheerer, G. W.; Lapertot, G.; Jaccard, D.
2015-03-01
CeAu2Si2 is a newly discovered pressure-induced heavy fermion superconductor, which shows very unusual interplay between superconductivity and magnetism under pressure. Here we compare the results of high-pressure measurements on single-crystalline CeAu2Si2 samples with different levels of disorder. It is found that while the magnetic properties are essentially sample independent, superconductivity is rapidly suppressed when the residual resistivity of the sample increases. We show that the depression of bulk Tc can be well understood in terms of pair breaking by nonmagnetic disorder, which strongly suggests an unconventional pairing state in pressurized CeAu2Si2 . Furthermore, increasing the level of disorder leads to the emergence of another phase transition at T* within the magnetic phase, which might be in competition with superconductivity.
Pressure-induced amorphization and orientational disorder in potash alum
NASA Astrophysics Data System (ADS)
Sakuntala, T.; Arora, Akhilesh K.; Shekar, N. V. Chandra; Sahu, P. Ch
2000-05-01
Pressure-induced amorphization in potassium aluminium sulphate dodecahydrate (potash alum) has been studied using Raman spectroscopy in a diamond anvil cell up to a pressure of 15 GPa. In potash alum, some of the sulphate ions are misoriented with their S-O bond pointing towards potassium rather than aluminium, leading to an `orientational disorder' which ranges from 10 to 24% at ambient conditions. The disorder is quantified from the intensities of the Raman lines characteristic of the two orientations. The samples with low initial disorder exhibit a sequence of two structural phase transitions occurring at 1.5 and 9 GPa respectively. The phase above 1.5 GPa, which could be pressure quenched to ambient conditions, is found to be free from orientational disorder. On the other hand, in the samples with high initial disorder, the disorder is found to grow as a function of pressure and beyond a critical value the system turns amorphous, which is confirmed from the disappearance of sharp diffraction peaks. In view of these results it is apparent that the orientational disorder is the driving mechanism of amorphization in potash alum. The different initial disorders in different samples are believed to arise from a combination of a dynamic disorder (equilibrium) and a static disorder arising from the defects. This defect could possibly be a missing molecule in the water octahedra around the potassium ion.
Transdermal deferoxamine prevents pressure-induced diabetic ulcers.
Duscher, Dominik; Neofytou, Evgenios; Wong, Victor W; Maan, Zeshaan N; Rennert, Robert C; Inayathullah, Mohammed; Januszyk, Michael; Rodrigues, Melanie; Malkovskiy, Andrey V; Whitmore, Arnetha J; Walmsley, Graham G; Galvez, Michael G; Whittam, Alexander J; Brownlee, Michael; Rajadas, Jayakumar; Gurtner, Geoffrey C
2015-01-01
There is a high mortality in patients with diabetes and severe pressure ulcers. For example, chronic pressure sores of the heels often lead to limb loss in diabetic patients. A major factor underlying this is reduced neovascularization caused by impaired activity of the transcription factor hypoxia inducible factor-1 alpha (HIF-1α). In diabetes, HIF-1α function is compromised by a high glucose-induced and reactive oxygen species-mediated modification of its coactivator p300, leading to impaired HIF-1α transactivation. We examined whether local enhancement of HIF-1α activity would improve diabetic wound healing and minimize the severity of diabetic ulcers. To improve HIF-1α activity we designed a transdermal drug delivery system (TDDS) containing the FDA-approved small molecule deferoxamine (DFO), an iron chelator that increases HIF-1α transactivation in diabetes by preventing iron-catalyzed reactive oxygen stress. Applying this TDDS to a pressure-induced ulcer model in diabetic mice, we found that transdermal delivery of DFO significantly improved wound healing. Unexpectedly, prophylactic application of this transdermal delivery system also prevented diabetic ulcer formation. DFO-treated wounds demonstrated increased collagen density, improved neovascularization, and reduction of free radical formation, leading to decreased cell death. These findings suggest that transdermal delivery of DFO provides a targeted means to both prevent ulcer formation and accelerate diabetic wound healing with the potential for rapid clinical translation.
Pressure induced reactions amongst calcium aluminate hydrate phases
Moon, Ju-hyuk; Oh, Jae Eun; Balonis, Magdalena; Glasser, Fredrik P.; Clark, Simon M.; Monteiro, Paulo J.M.
2011-06-15
The compressibilities of two AFm phases (straetlingite and calcium hemicarboaluminate hydrate) and hydrogarnet were obtained up to 5 GPa by using synchrotron high-pressure X-ray powder diffraction with a diamond anvil cell. The AFm phases show abrupt volume contraction regardless of the molecular size of the pressure-transmitting media. This volume discontinuity could be associated to a structural transition or to the movement of the weakly bound interlayer water molecules in the AFm structure. The experimental results seem to indicate that the pressure-induced dehydration is the dominant mechanism especially with hygroscopic pressure medium. The Birch-Murnaghan equation of state was used to compute the bulk modulus of the minerals. Due to the discontinuity in the pressure-volume diagram, a two stage bulk modulus of each AFm phase was calculated. The abnormal volume compressibility for the AFm phases caused a significant change to their bulk modulus. The reliability of this experiment is verified by comparing the bulk modulus of hydrogarnet with previous studies.
Nature of Pressure-induced Insulating States in Simple Metals
NASA Astrophysics Data System (ADS)
Naumov, Ivan; Hemley, Russell
As experimentally established, all the alkali metals and heavy alkaline earth metals (Ca, Sr and Ba) become progressively less conductive on compression, at least up to some critical limit over a broad pressure range. Of these metals, Li and Na clearly undergo pressure-induced metal-insulator transitions, which may also be called reverse Mott transitions. Here, using group theory arguments and first-principles calculations, we show that such transitions can be understood in terms of band representations introduced by Zak. The valence bands in the insulating states are described by simple and composite band representations constructed from localized Wannier functions centered on points unoccupied by atoms. The character of the Wannier functions is closely related to the degree of s-p(-d) hybridization and reflects multi-center chemical bonding in these insulating states. The conditions under which an insulating state is allowed for structures having an integer number of atoms per primitive unit cell as well as re-entrant (i.e., metal-insulator-metal) transition sequences are detailed, resulting in predictions of semimetallic phases with flat surface states. The general principles developed are tested and applied to the alkali and alkaline earth metals, including elements where high-pressure insulating phases have been identified or reported (e.g., Li, Na, and Ca). This research was supported by EFree, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award DESC0001057.
Pressure-induced phase transitions and metallization in VO2
NASA Astrophysics Data System (ADS)
Bai, Ligang; Li, Quan; Corr, Serena A.; Meng, Yue; Park, Changyong; Sinogeikin, Stanislav V.; Ko, Changhyun; Wu, Junqiao; Shen, Guoyin
2015-03-01
We report the results of pressure-induced phase transitions and metallization in VO2 based on synchrotron x-ray diffraction, electrical resistivity, and Raman spectroscopy. Our isothermal compression experiments at room temperature and 383 K show that the room temperature monoclinic phase (M 1 ,P 21/c ) and the high-temperature rutile phase (R ,P 42/m n m ) of VO2 undergo phase transitions to a distorted M 1 monoclinic phase (M 1' ,P 21/c ) above 13.0 GPa and to an orthorhombic phase (CaCl2-like, P n n m ) above 13.7 GPa, respectively. Upon further compression, both high-pressure phases transform into a new phase (phase X ) above 34.3 and 38.3 GPa at room temperature and 383 K, respectively. The room temperature M 1 -M 1' phase transition structurally resembles the R -CaCl2 phase transition at 383 K, suggesting a second-order displacive type of transition. Contrary to previous studies, our electrical resistivity results, Raman measurements, as well as ab initio calculations indicate that the new phase X , rather than the M 1' phase, is responsible for the metallization under pressure. The metallization mechanism is discussed based on the proposed crystal structure.
Transdermal deferoxamine prevents pressure-induced diabetic ulcers
Duscher, Dominik; Neofytou, Evgenios; Wong, Victor W.; Maan, Zeshaan N.; Rennert, Robert C.; Januszyk, Michael; Rodrigues, Melanie; Malkovskiy, Andrey V.; Whitmore, Arnetha J.; Galvez, Michael G.; Whittam, Alexander J.; Brownlee, Michael; Rajadas, Jayakumar; Gurtner, Geoffrey C.
2015-01-01
There is a high mortality in patients with diabetes and severe pressure ulcers. For example, chronic pressure sores of the heels often lead to limb loss in diabetic patients. A major factor underlying this is reduced neovascularization caused by impaired activity of the transcription factor hypoxia inducible factor-1 alpha (HIF-1α). In diabetes, HIF-1α function is compromised by a high glucose-induced and reactive oxygen species-mediated modification of its coactivator p300, leading to impaired HIF-1α transactivation. We examined whether local enhancement of HIF-1α activity would improve diabetic wound healing and minimize the severity of diabetic ulcers. To improve HIF-1α activity we designed a transdermal drug delivery system (TDDS) containing the FDA-approved small molecule deferoxamine (DFO), an iron chelator that increases HIF-1α transactivation in diabetes by preventing iron-catalyzed reactive oxygen stress. Applying this TDDS to a pressure-induced ulcer model in diabetic mice, we found that transdermal delivery of DFO significantly improved wound healing. Unexpectedly, prophylactic application of this transdermal delivery system also prevented diabetic ulcer formation. DFO-treated wounds demonstrated increased collagen density, improved neovascularization, and reduction of free radical formation, leading to decreased cell death. These findings suggest that transdermal delivery of DFO provides a targeted means to both prevent ulcer formation and accelerate diabetic wound healing with the potential for rapid clinical translation. PMID:25535360
Pressure-induced activity loss in solid state catalase.
Wurster, D E; Ternik, R L
1995-02-01
The pressure-induced reductions in the activities of a number of enzymes in the solution state, and more recently in the solid state, have been reported. To further investigate the effect of pressure on proteins in the solid state, the enzyme catalase was used as a model. Compacts containing 150.0 +/- 0.2 mg of catalase powder were prepared on instrumented laboratory presses using various compaction pressures between 0 and 669 MPa. After compaction, a spectrophotometric assay was utilized to determine the pseudo-first-order rate constants for the catalase-catalyzed decomposition of hydrogen peroxide. These rate constants were used to calculate the change in catalase activity. Results indicated a loss in catalase activity of up to 30% at compaction pressures of 251 MPa or greater. While the mechanism which produces the loss of enzyme activity is not clear, a strong linear correlation between enzyme activity and compaction pressure was seen over the range of pressures (0-251 MPa) where the decrease in activity occurred. In addition, compact densities were calculated and correlated to enzyme activity values. This correlation did not appear to be as strong. PMID:7738799
High-pressure-induced water penetration into 3-isopropylmalate dehydrogenase
Nagae, Takayuki; Kawamura, Takashi; Chavas, Leonard M. G.; Niwa, Ken; Hasegawa, Masashi; Kato, Chiaki; Watanabe, Nobuhisa
2012-03-01
Structures of 3-isopropylmalate dehydrogenase were determined at pressures ranging from 0.1 to 650 MPa. Comparison of these structures gives a detailed picture of the swelling of a cavity at the dimer interface and the generation of a new cleft on the molecular surface, which are accompanied by water penetration. Hydrostatic pressure induces structural changes in proteins, including denaturation, the mechanism of which has been attributed to water penetration into the protein interior. In this study, structures of 3-isopropylmalate dehydrogenase (IPMDH) from Shewanella oneidensis MR-1 were determined at about 2 Å resolution under pressures ranging from 0.1 to 650 MPa using a diamond anvil cell (DAC). Although most of the protein cavities are monotonically compressed as the pressure increases, the volume of one particular cavity at the dimer interface increases at pressures over 340 MPa. In parallel with this volume increase, water penetration into the cavity could be observed at pressures over 410 MPa. In addition, the generation of a new cleft on the molecular surface accompanied by water penetration could also be observed at pressures over 580 MPa. These water-penetration phenomena are considered to be initial steps in the pressure-denaturation process of IPMDH.
Superconducting quantum interference device detection of magnetically tagged micro-organisms
NASA Astrophysics Data System (ADS)
Grossman, Helene L.; Lee, SeungKyun; Myers, Whittier R.; Chemla, Yann R.; Poon, Yan; Cho, H. M.; McDermott, Robert; Stevens, Raymond C.; Alper, Mark; Clarke, John
2002-02-01
A fast and versatile technique has been developed for detecting small quantities of specific microorganisms or molecules with high specificity. The target analytes are bound to a substrate and placed in the measurement cell of a microscope based on a high-transition temperature Superconducting Quantum Interference Device (SQUID). A solution containing nanometer-size magnetite particles, coated with antibodies specific to the target, is added. The particles, which bind to the target via the antibody- antigen interaction, are superparamagnetic with a Neel relaxation time of ~1s. A pulsed magnetic field aligns the dipole moments, and the SQUID measures the magnetic relaxation signal when the field is turned off. Unbound magnetic particles relax rapidly (~15microsecond(s) ) by Brownian rotation and are not detected. On the other hand, particles bound to targets cannot rotate and instead relax slowly by the Neel mechanism. As a result, only bound particles contribute to the signal, allowing for quantification of the number of targets present without the need for a wash step. The current system can detect as few as 2000 magnetic particles. This technique could be used to detect a wide range of bacteria, viruses, and molecules, with potential applications in the food industry, clinical settings, or research laboratories.
Wu, Wei
2014-07-23
The magnetic properties of a theoretically designed molecular chain structure CuCoPc2, in which copper-phthalocyanine (CuPc) and cobalt-phthalocyanine (CoPc) alternate, have been investigated across a range of chain structures. The computed exchange interaction for the α-phase CuCoPc2 is ∼ 5 K (ferromagnetic), in strong contrast to the anti-ferromagnetic interaction recently observed in CuPc and CoPc. The computed exchange interactions are strongly dependent on the stacking angle but weakly on the sliding angle, and peak at 20 K (ferromagnetic). These ferromagnetic interactions are expected to arise from direct exchange with the strong suppression of super-exchange interaction. These first-principles calculations show that π-conjugated molecules, such as phthalocyanine, could be used as building blocks for the design of magnetic materials. This therefore extends the concept of quantum metamaterials further into magnetism. The resulting new magnetic materials could find applications in the studies such as organic spintronics.
Optical signatures of electric-field-driven magnetic phase transitions in graphene quantum dots
NASA Astrophysics Data System (ADS)
Basak, Tista; Shukla, Alok
2016-06-01
Experimental challenges in identifying various types of magnetic ordering in graphene quantum dots (QDs) pose a major hurdle in the application of these nanostructures for spintronic devices. Based upon phase diagrams obtained by employing the π -electron Pariser-Parr-Pople (PPP) model Hamiltonian, we demonstrate that the magnetic states undergo phase transition under the influence of an external electric field. Our calculations of the electroabsorption spectra of these QDs indicate that the spectrum in question carries strong signatures of their magnetic state (FM vs AFM), thus suggesting the possibility of an all-optical characterization of their magnetic nature. Further, the gaps for the up and the down spins are the same in the absence of an external electric field, both for the antiferromagnetic (AFM) and the ferromagnetic (FM) states of QDs. But, once the QDs are exposed to a suitably directed external electric field, gaps for different spins split and exhibit distinct variations with respect to the strength of the field. The nature of variation exhibited by the energy gaps corresponding to the up and down spins is different for the AFM and FM configurations of QDs. This selective manipulation of the spin-polarized gap splitting by an electric field in finite graphene nanostructures can open up new frontiers in the design of graphene-based spintronic devices.
Wu, Wei
2014-07-23
The magnetic properties of a theoretically designed molecular chain structure CuCoPc2, in which copper-phthalocyanine (CuPc) and cobalt-phthalocyanine (CoPc) alternate, have been investigated across a range of chain structures. The computed exchange interaction for the α-phase CuCoPc2 is ∼ 5 K (ferromagnetic), in strong contrast to the anti-ferromagnetic interaction recently observed in CuPc and CoPc. The computed exchange interactions are strongly dependent on the stacking angle but weakly on the sliding angle, and peak at 20 K (ferromagnetic). These ferromagnetic interactions are expected to arise from direct exchange with the strong suppression of super-exchange interaction. These first-principles calculations show that π-conjugated molecules, such as phthalocyanine, could be used as building blocks for the design of magnetic materials. This therefore extends the concept of quantum metamaterials further into magnetism. The resulting new magnetic materials could find applications in the studies such as organic spintronics. PMID:24990182
NASA Astrophysics Data System (ADS)
Lai, Wenxi; Yang, Wen
2015-10-01
We consider theoretically a magnetic impurity spin driven by polarized electrons tunneling through a double-quantum-dot system. The spin-blockade effect and spin conservation in the system make the magnetic impurity sufficiently interact with each transferring electron. As a result, a single collected electron carries information about spin change of the magnetic impurity. The scheme may develop all-electrical manipulation of magnetic atoms by means of single electrons, which is significant for the implementation of scalable logical gates in information processing systems.
Quantum spin ices and magnetic states from dipolar-octupolar doublets on the pyrochlore lattice
NASA Astrophysics Data System (ADS)
Chen, Gang
We consider a class of electron systems in which dipolar-octupolar Kramers doublets arise on the pyrochlore lattice. In the localized limit, the Kramers doublets are described by the effective spin 1/2 pseudospins. The most general nearest-neighbor exchange model between these pseudospins is the XYZ model. In additional to dipolar ordered and octupolar ordered magnetic states, we show that this XYZ model exhibits two distinct quantum spin ice (QSI) phases, that we dub dipolar QSI and octupolar QSI. These two QSIs are distinct symmetry enriched U(1) quantum spin liquids, enriched by the lattice symmetry. Moreover, the XYZ model is absent from the notorious sign problem for a quantum Monte Carlo simulation in a large parameter space. We discuss the potential relevance to real material systems such as Dy2Ti2O7, Nd2Zr2O7, Nd2Hf2O7, Nd2Ir2O7, Nd2Sn2O7 and Ce2Sn2O7. chggst@gmail.com, Refs: Y-P Huang, G Chen, M Hermele, Phys. Rev. Lett. 112, 167203 (2014).
Manipulation of the nuclear spin ensemble in a quantum dot with chirped magnetic resonance pulses
NASA Astrophysics Data System (ADS)
Munsch, Mathieu; Wüst, Gunter; Kuhlmann, Andreas V.; Xue, Fei; Ludwig, Arne; Reuter, Dirk; Wieck, Andreas D.; Poggio, Martino; Warburton, Richard J.
2014-09-01
The nuclear spins in nanostructured semiconductors play a central role in quantum applications. The nuclear spins represent a useful resource for generating local magnetic fields but nuclear spin noise represents a major source of dephasing for spin qubits. Controlling the nuclear spins enhances the resource while suppressing the noise. NMR techniques are challenging: the group III and V isotopes have large spins with widely different gyromagnetic ratios; in strained material there are large atom-dependent quadrupole shifts; and nanoscale NMR is hard to detect. We report NMR on 100,000 nuclear spins of a quantum dot using chirped radiofrequency pulses. Following polarization, we demonstrate a reversal of the nuclear spin. We can flip the nuclear spin back and forth a hundred times. We demonstrate that chirped NMR is a powerful way of determining the chemical composition, the initial nuclear spin temperatures and quadrupole frequency distributions for all the main isotopes. The key observation is a plateau in the NMR signal as a function of sweep rate: we achieve inversion at the first quantum transition for all isotopes simultaneously. These experiments represent a generic technique for manipulating nanoscale inhomogeneous nuclear spin ensembles and open the way to probe the coherence of such mesoscopic systems.
Carrier relaxation in (In,Ga)As quantum dots with magnetic field-induced anharmonic level structure
NASA Astrophysics Data System (ADS)
Kurtze, H.; Bayer, M.
2016-07-01
Sophisticated models have been worked out to explain the fast relaxation of carriers into quantum dot ground states after non-resonant excitation, overcoming the originally proposed phonon bottleneck. We apply a magnetic field along the quantum dot heterostructure growth direction to transform the confined level structure, which can be approximated by a Fock-Darwin spectrum, from a nearly equidistant level spacing at zero field to strong anharmonicity in finite fields. This changeover leaves the ground state carrier population rise time unchanged suggesting that fast relaxation is maintained upon considerable changes of the level spacing. This corroborates recent models explaining the relaxation by polaron formation in combination with quantum kinetic effects.
NASA Astrophysics Data System (ADS)
Ostahie, B.; Aldea, A.
2016-02-01
Spectral and transport properties of electrons in confined phosphorene systems are investigated in a five hopping parameter tight-binding model, using analytical and numerical techniques. The main emphasis is on the properties of the topological edge states accommodated by the quasiflat band that characterizes the phosphorene energy spectrum. We show, in the particular case of phosphorene, how the breaking of the bipartite lattice structure gives rise to the electron-hole asymmetry of the energy spectrum. The properties of the topological edge states in the zigzag nanoribbons are analyzed under different aspects: degeneracy, localization, extension in the Brillouin zone, dispersion of the quasiflat band in magnetic field. The finite-size phosphorene plaquette exhibits a Hofstadter-type spectrum made up of two unequal butterflies separated by a gap, where a quasiflat band composed of zigzag edge states is located. The transport properties are investigated by simulating a four-lead Hall device (importantly, all leads are attached on the same zigzag side), and using the Landauer-Büttiker formalism. We find out that the chiral edge states due to the magnetic field yield quantum Hall plateaus, but the topological edge states in the gap do not support the quantum Hall effect and prove a dissipative behavior. By calculating the complex eigenenergies of the non-Hermitian effective Hamiltonian that describes the open system (plaquette+leads), we prove the superradiance effect in the energy range of the quasiflat band, with consequences for the density of states and electron transmission properties.
Continuous and discontinuous quantum phase transitions in a model two-dimensional magnet
Haravifard, S.; Banerjee, A.; Lang, J. C.; Srajer, G.; Silevitch, D. M.; Gaulin, B. D.; Dabkowska, H. A.; Rosenbaum, T. F.
2012-01-01
The Shasty–Sutherland model, which consists of a set of spin 1/2 dimers on a 2D square lattice, is simple and soluble but captures a central theme of condensed matter physics by sitting precariously on the quantum edge between isolated, gapped excitations and collective, ordered ground states. We compress the model Shastry–Sutherland material, SrCu2(BO3)2, in a diamond anvil cell at cryogenic temperatures to continuously tune the coupling energies and induce changes in state. High-resolution X-ray measurements exploit what emerges as a remarkably strong spin-lattice coupling to both monitor the magnetic behavior and the absence or presence of structural discontinuities. In the low-pressure spin-singlet regime, the onset of magnetism results in an expansion of the lattice with decreasing temperature, which permits a determination of the pressure-dependent energy gap and the almost isotropic spin-lattice coupling energies. The singlet-triplet gap energy is suppressed continuously with increasing pressure, vanishing completely by 2 GPa. This continuous quantum phase transition is followed by a structural distortion at higher pressure. PMID:22308373
Continuous and discontinuous quantum phase transitions in a model two-dimensional magnet.
Haravifard, S; Banerjee, A; Lang, J C; Srajer, G; Silevitch, D M; Gaulin, B D; Dabkowska, H A; Rosenbaum, T F
2012-02-14
The Shasty-Sutherland model, which consists of a set of spin 1/2 dimers on a 2D square lattice, is simple and soluble but captures a central theme of condensed matter physics by sitting precariously on the quantum edge between isolated, gapped excitations and collective, ordered ground states. We compress the model Shastry-Sutherland material, SrCu(2)(BO(3))(2), in a diamond anvil cell at cryogenic temperatures to continuously tune the coupling energies and induce changes in state. High-resolution X-ray measurements exploit what emerges as a remarkably strong spin-lattice coupling to both monitor the magnetic behavior and the absence or presence of structural discontinuities. In the low-pressure spin-singlet regime, the onset of magnetism results in an expansion of the lattice with decreasing temperature, which permits a determination of the pressure-dependent energy gap and the almost isotropic spin-lattice coupling energies. The singlet-triplet gap energy is suppressed continuously with increasing pressure, vanishing completely by 2 GPa. This continuous quantum phase transition is followed by a structural distortion at higher pressure. PMID:22308373
Intrinsic Localized Modes in Quantum Ferromagnetic XXZ Chains in an Oblique Magnetic Field
NASA Astrophysics Data System (ADS)
Li, De-Jun
2016-02-01
A semiclassical study of intrinsic localized spin-wave modes in a one-dimensional quantum ferromagnetic XXZ chain in an oblique magnetic field is presented in this paper. We quantize the model Hamiltonian by introducing the Dyson-Maleev transformation, and adopt the coherent state representation as the basic representation of the system. By means of the method of multiple scales combined with a quasidiscreteness approximation, the equation of motion for the coherent-state amplitude can be reduced to the standard nonlinear Schrödinger equation. It is found that, at the center of the Brillouin zone, when θ < θ c a bright intrinsic localized spin-wave mode appears below the bottom of the magnon frequency band and when θ > θ c a dark intrinsic localized spin-wave resonance mode can occur above the bottom of the magnon frequency band. In other words, the switch between the bright and dark intrinsic localized spin-wave modes can be controlled via varying the angle of the magnetic field. This result has potential applications in quantum information storage. In addition, we find that, at the boundary of the Brillouin zone, the system can only produce a dark intrinsic localized spin-wave mode, whose eigenfrequency is above the upper of the magnon frequency band.
NASA Astrophysics Data System (ADS)
Wood, James D. A.; Broadway, David A.; Hall, Liam T.; Stacey, Alastair; Simpson, David A.; Tetienne, Jean-Philippe; Hollenberg, Lloyd C. L.
2016-10-01
We demonstrate an all-optical approach of nanoscale magnetic resonance (MR) spectroscopy whereby quantum relaxation (T1) of a single probe spin in diamond is monitored during a precise static magnetic field sweep to construct a spectrum of the surrounding spin environment. The method is inherently noninvasive as it involves no driving fields, and instead relies on the natural resonance between the quantum probe and target spins. As a proof of concept, we measure the T1-MR spectra across a wide band [megahertz (MHz) to gigahertz (GHz)] of a small ensemble of 14N impurities surrounding a single probe spin, providing information on both electron spin transitions (in the GHz range) and nuclear spin transitions (in the MHz range) of the 14N spin targets. Analysis of the T1-MR spectrum reveals that the electron spin transitions are probed via dipole interactions with the probe, while the relatively weak nuclear spin resonances are dramatically enhanced by hyperfine coupling in an electron-mediated process. With a projected sensitivity to external single-proton spins, this work establishes T1-MR as a powerful noninvasive wide-band technique for nanoscale MR spectroscopy.
Anomalous Dynamical Line Shapes in a Quantum Magnet at Finite Temperature
Tennant D. A.; James A.; Lake, B.; Essler, F.H.L.; Notbohm, S.; Mikeska, H.-J.; Fielden, J.; Kogerler,, P.; Canfield, P.C.; Telling, M.T.F.
2012-01-04
The effect of thermal fluctuations on the dynamics of a gapped quantum magnet is studied using inelastic neutron scattering on copper nitrate, a model material for the spin-1/2, one-dimensional (1D) bond alternating Heisenberg chain. A large, highly deuterated, single-crystal sample of copper nitrate is produced using a solution growth method and measurements are made using the high-resolution backscattering spectrometer OSIRIS at the ISIS Facility. Theoretical calculations and numerical analysis are combined to interpret the physical origin of the thermal effects observed in the magnetic spectra. The primary observations are (1) a thermally induced central peak due to intraband scattering, which is similar to Villain scattering familiar from soliton systems in 1D, and (2) the one-magnon quasiparticle pole is seen to develop with temperature into an asymmetric continuum of scattering. We relate this asymmetric line broadening to a thermal strongly correlated state caused by hard-core constraints and quasiparticle interactions. These findings are a counter example to recent assertions of the universality of line broadening in 1D systems and are applicable to a broad range of quantum systems.
Size dependent magnetic and optical properties in diamond shaped graphene quantum dots: A DFT study
NASA Astrophysics Data System (ADS)
Das, Ritwika; Dhar, Namrata; Bandyopadhyay, Arka; Jana, Debnarayan
2016-12-01
The magnetic and optical properties of diamond shaped graphene quantum dots (DSGQDs) have been investigated by varying their sizes with the help of density functional theory (DFT). The study of density of states (DOS) has revealed that the Fermi energy decreases with increase in sizes (number of carbon atoms). The intermediate structure with 30 carbon atoms shows the highest magnetic moment (8 μB, μB being the Bohr magneton). The shifting of optical transitions to higher energy in smallest DSGQD (16 carbon atoms) bears the signature of stronger quantum confinement. However, for the largest structure (48 carbon atoms) multiple broad peaks appear in case of parallel polarization and in this case electron energy loss spectra (EELS) peak (in the energy range 0-5 eV) is sharp in nature (compared to high energy peak). This may be attributed to π plasmon and the broad peak (in the range 10-16 eV) corresponds to π + σ plasmon. A detail calculation of the Raman spectra has indicated some prominent mode of vibrations which can be used to characterize these structures (with hydrogen terminated dangling bonds). We think that these theoretical observations can be utilized for novel device designs involving DSGQDs.
NASA Astrophysics Data System (ADS)
Lee, S.; Titova, L. V.; Furdyna, Jacek K.; Dobrowolska, M.
2000-03-01
It has been recently reported that the properties of self-organized CdSe quantum dots (QDs) on ZnSe change significantly when they are grown on ZnMnSe spacers separating CdSe form ZnSe.[1] To explore this effect futher, we have prepared a series of samples by depositing one monolayer (ML) of CdSe on ZnMnSe spacer layers of different thickness and different Mn concentration. The system is then capped with ZnSe. The band structure for this geometry results in an asymmetric quantum structure, where the 1 ML thick CdSe acts as a "well" between barriers comprised of ZnSe on side, and ZnMnSe on the other. When a magnetic field is applied, the Zeeman splitting of the band edges in ZnMnSe spacer moves the position of the wave function toward or away from the spacer, depending on spin orientation. Such spin-selective repositioning of the wave functions is fully confirmed by magnetic field dependence of ground state exciton transitions observed in PL. This work was supported by NSF Grant DMR 9705064. [1]C.S. Kim et.al., 9th International conference on II-VI compounds, Kyoto, Nov. 1-5, 1999.
NASA Astrophysics Data System (ADS)
Ge, Song
In this dissertation, I present the development of a SQUID (Superconducting Quantum Interference Device) imaging system using targeted magnetic nanoparticles (NPs) as contrast agents. The contrast agents are functionalized for targeting by the conjugation of the magnetic NPs to folic acid (FA) molecules on dendrimer scaffolds. Cellular internalization is accomplished through the high-affinity folic acid receptors (FARs), which are overexpressed in various human carcinomas. SQUID can be applied to detect signals from the magnetic cores of the contrast agents and hence diagnose the tumor. Based on the magnetic properties of the magnetic NPs, two detection methods were developed: remanence and magnetorelaxometry (MRX). The remanence measurement-based method detects magnetic NPs that are sufficiently large and possess long relaxation time. Samples were vertically oscillated and horizontally translated each in one-dimension. The system was calibrated with gamma-Fe2O3 NPs (mean diameter 25 nm) and the detection limit was found to be 10 ng at a distance of 1.7 cm and the spatial resolution was ˜1 cm. A theoretical model of this system was proposed and applied to image reconstruction of scanned phantoms with two NP injection spots. The developed SQUID system can determine not only the amount and horizontal position of the NPs, but also their depth in the phantoms. The MRX technique utilizes the NPs superparamagnetic property and records their time course magnetic decay. The system was investigated by using a number of iron oxide NP products with different mean diameters. The results showed that the MRX signal intensity is sensitively dependent on the size of the NPs. The best detection limit of 300 ng of total iron content was found on using a d = 12 nm Fe3O4 NP sample and this result was supported by computer simulations. To produce magnetic NPs for the MRX study, a synthetic approach of size-controllable Fe3O4 NPs was developed. Accordingly, the magnetic property can be
Tokiwa, Y.; Yamashita, T.; Udagawa, M.; Kittaka, S.; Sakakibara, T; Terazawa, D.; Shimoyama, Y.; Terashima, T.; Yasui, Y.; Shibauchi, T.; Matsuda, Y.
2016-01-01
The low-energy elementary excitations in frustrated quantum magnets have fascinated researchers for decades. In frustrated Ising magnets on a pyrochlore lattice possessing macroscopically degenerate spin-ice ground states, the excitations have been discussed in terms of classical magnetic monopoles, which do not contain quantum fluctuations. Here we report unusual behaviours of magneto-thermal conductivity in the disordered spin-liquid regime of pyrochlore Yb2Ti2O7, which hosts frustrated spin-ice correlations with large quantum fluctuations owing to pseudospin-1/2 of Yb ions. The analysis of the temperature and magnetic field dependencies shows the presence of gapped elementary excitations. We find that the gap energy is largely suppressed from that expected in classical monopoles. Moreover, these excitations propagate a long distance without being scattered, in contrast to the diffusive nature of classical monopoles. These results suggests the emergence of highly itinerant quantum magnetic monopole, which is a heavy quasiparticle that propagates coherently in three-dimensional spin liquids. PMID:26912080
Tokiwa, Y; Yamashita, T; Udagawa, M; Kittaka, S; Sakakibara, T; Terazawa, D; Shimoyama, Y; Terashima, T; Yasui, Y; Shibauchi, T; Matsuda, Y
2016-01-01
The low-energy elementary excitations in frustrated quantum magnets have fascinated researchers for decades. In frustrated Ising magnets on a pyrochlore lattice possessing macroscopically degenerate spin-ice ground states, the excitations have been discussed in terms of classical magnetic monopoles, which do not contain quantum fluctuations. Here we report unusual behaviours of magneto-thermal conductivity in the disordered spin-liquid regime of pyrochlore Yb2Ti2O7, which hosts frustrated spin-ice correlations with large quantum fluctuations owing to pseudospin-1/2 of Yb ions. The analysis of the temperature and magnetic field dependencies shows the presence of gapped elementary excitations. We find that the gap energy is largely suppressed from that expected in classical monopoles. Moreover, these excitations propagate a long distance without being scattered, in contrast to the diffusive nature of classical monopoles. These results suggests the emergence of highly itinerant quantum magnetic monopole, which is a heavy quasiparticle that propagates coherently in three-dimensional spin liquids. PMID:26912080
Ding, Ke; Jing, Lihong; Liu, Chunyan; Hou, Yi; Gao, Mingyuan
2014-02-01
Magnetically engineered Cd-free CuInS2@ZnS:Mn quantum dots (QDs) were designed, synthesized, and evaluated as potential dual-modality probes for fluorescence and magnetic resonance imaging (MRI) of tumors in vivo. The synthesis of Mn-doped core-shell structured CuInS2@ZnS mainly comprised three steps, i.e., the preparation of fluorescent CuInS2 seeds, the particle surface coating of ZnS, and the Mn-doping of the ZnS shells. Systematic spectroscopy studies were carried out to illustrate the impacts of ZnS coating and the following Mn-doping on the optical properties of the QDs. In combination with conventional fluorescence, fluorescence excitation, and time-resolved fluorescence measurements, the structure of CuInS2@ZnS:Mn QDs prepared under optimized conditions presented a Zn gradient CuInS2 core and a ZnS outer shell, while Mn ions were mainly located in the ZnS shell, which well balanced the optical and magnetic properties of the resultant QDs. For the following in vivo imaging experiments, the hydrophobic CuInS2@ZnS:Mn QDs were transferred into water upon ligand exchange reactions by replacing the 1-dodecanethiol ligand with dihydrolipoic acid-poly(ethylene glycol) (DHLA-PEG) ligand. The MTT assays based on HeLa cells were carried out to evaluate the cytotoxicity of the current Cd-free CuInS2@ZnS:Mn QDs for comparing with that of water soluble CdTe QDs. Further in vivo fluorescence and MR imaging experiments suggested that the PEGylated CuInS2@ZnS:Mn QDs could well target both subcutaneous and intraperitoneal tumors in vivo.
Masuda, Hidetoshi; Sakai, Hideaki; Tokunaga, Masashi; Yamasaki, Yuichi; Miyake, Atsushi; Shiogai, Junichi; Nakamura, Shintaro; Awaji, Satoshi; Tsukazaki, Atsushi; Nakao, Hironori; Murakami, Youichi; Arima, Taka-hisa; Tokura, Yoshinori; Ishiwata, Shintaro
2016-01-01
For the innovation of spintronic technologies, Dirac materials, in which low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems because of the fascinating magnetotransport associated with extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid. We report a bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi2, in which field-controllable Eu magnetic order significantly suppresses the interlayer coupling between the Bi layers with Dirac fermions. In addition to the high mobility of more than 10,000 cm2/V s, Landau level splittings presumably due to the lifting of spin and valley degeneracy are noticeable even in a bulk magnet. These results will pave a route to the engineering of magnetically functionalized Dirac materials. PMID:27152326
Masuda, Hidetoshi; Sakai, Hideaki; Tokunaga, Masashi; Yamasaki, Yuichi; Miyake, Atsushi; Shiogai, Junichi; Nakamura, Shintaro; Awaji, Satoshi; Tsukazaki, Atsushi; Nakao, Hironori; Murakami, Youichi; Arima, Taka-hisa; Tokura, Yoshinori; Ishiwata, Shintaro
2016-01-01
For the innovation of spintronic technologies, Dirac materials, in which low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems because of the fascinating magnetotransport associated with extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid. We report a bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi2, in which field-controllable Eu magnetic order significantly suppresses the interlayer coupling between the Bi layers with Dirac fermions. In addition to the high mobility of more than 10,000 cm(2)/V s, Landau level splittings presumably due to the lifting of spin and valley degeneracy are noticeable even in a bulk magnet. These results will pave a route to the engineering of magnetically functionalized Dirac materials. PMID:27152326
Pressure-induced phase transition and polymerization of tetracyanoethylene (TCNE)
NASA Astrophysics Data System (ADS)
Tomasino, Dane; Chen, Jing-Yin; Kim, Minesob; Yoo, Choong-Shik
2013-03-01
We have studied the pressure-induced physical and chemical transformations of tetracyanoethylene (TCNE or C6N4) in diamond anvil cells using micro-Raman spectroscopy, laser-heating, emission spectroscopy, and synchrotron x-ray diffraction. The results indicate that TCNE in a quasi-hydrostatic condition undergoes a shear-induced phase transition at 10 GPa and then a chemical change to two-dimensional (2D) C=N polymers above 14 GPa. These phase and chemical transformations depend strongly on the state of stress in the sample and occur sluggishly in non-hydrostatic conditions over a large pressure range between 7 and 14 GPa. The x-ray diffraction data indicate that the phase transition occurs isostructurally within the monoclinic structure (P21/c) without any apparent volume discontinuity and the C=N polymer is highly disordered but remains stable to 60 GPa—the maximum pressure studied. On the other hand, laser-heating of the C=N polymer above 25 GPa further converts to a theoretically predicted 3D C-N network structure, evident from an emergence of new Raman νs(C-N) at 1404 cm-1 at 25 GPa and the visual appearance of translucent solid. The C-N product is, however, unstable upon pressure unloading below 10 GPa, resulting in a grayish powder that can be considered as nano-diamonds with high-nitrogen content at ambient pressure. The C-N product shows a strong emission line centered at 640 nm at 30 GPa, which linearly shifts toward shorter wavelength at the rate of -1.38 nm/GPa. We conjecture that the observed red shift upon unloading pressure is due to increase of defects in the C-N product and thereby weakening of C-N bonds.
Quantum magnetism of spinor bosons in optical lattices with synthetic non-Abelian gauge fields
NASA Astrophysics Data System (ADS)
Sun, Fadi; Ye, Jinwu; Liu, Wu-Ming
2015-10-01
We study quantum magnetism of interacting spinor bosons at integer fillings hopping in a square lattice in the presence of non-Abelian gauge fields. In the strong-coupling limit, this leads to the rotated ferromagnetic Heisenberg model, which is a new class of quantum spin model. We introduce Wilson loops to characterize frustrations and gauge equivalent classes. For a special equivalent class, we identify a spin-orbital entangled commensurate ground state. It supports not only commensurate magnons, but also a gapped elementary excitation: incommensurate magnons with two gap minima continuously tuned by the spin-orbit coupling (SOC) strength. At low temperatures, these magnons lead to dramatic effects in many physical quantities such as density of states, specific heat, magnetization, uniform susceptibility, staggered susceptibility, and various spin-correlation functions. The commensurate magnons lead to a pinned central peak in the angle-resolved light or atom Bragg spectroscopy. However, the incommensurate magnons split it into two located at their two gap minima. At high temperatures, the transverse spin-structure factors depend on the SOC strength explicitly. The whole set of Wilson loops can be mapped out by measuring the specific heat at the corresponding orders in the high-temperature expansion. We argue that one gauge may be realized in current experiments and other gauges may also be realized in future experiments. The results achieved along the exact solvable line sets up the stage to investigate dramatic effects when tuning away from it by various means. We sketch the crucial roles to be played by these magnons at other equivalent classes, with spin anisotropic interactions and in the presence of finite magnetic fields. Various experimental detections of these phenomena are discussed.
Magnetic quantum tunneling: key insights from multi-dimensional high-field EPR.
Lawrence, J; Yang, E-C; Hendrickson, D N; Hill, S
2009-08-21
Multi-dimensional high-field/frequency electron paramagnetic resonance (HFEPR) spectroscopy is performed on single-crystals of the high-symmetry spin S = 4 tetranuclear single-molecule magnet (SMM) [Ni(hmp)(dmb)Cl](4), where hmp(-) is the anion of 2-hydroxymethylpyridine and dmb is 3,3-dimethyl-1-butanol. Measurements performed as a function of the applied magnetic field strength and its orientation within the hard-plane reveal the four-fold behavior associated with the fourth order transverse zero-field splitting (ZFS) interaction, (1/2)B(S + S), within the framework of a rigid spin approximation (with S = 4). This ZFS interaction mixes the m(s) = +/-4 ground states in second order of perturbation, generating a sizeable (12 MHz) tunnel splitting, which explains the fast magnetic quantum tunneling in this SMM. Meanwhile, multi-frequency measurements performed with the field parallel to the easy-axis reveal HFEPR transitions associated with excited spin multiplets (S < 4). Analysis of the temperature dependence of the intensities of these transitions enables determination of the isotropic Heisenberg exchange constant, J = -6.0 cm(-1), which couples the four spin s = 1 Ni(II) ions within the cluster, as well as a characterization of the ZFS within excited states. The combined experimental studies support recent work indicating that the fourth order anisotropy associated with the S = 4 state originates from second order ZFS interactions associated with the individual Ni(II) centers, but only as a result of higher-order processes that occur via S-mixing between the ground state and higher-lying (S < 4) spin multiplets. We argue that this S-mixing plays an important role in the low-temperature quantum dynamics associated with many other well known SMMs.
Pressure-induced change of the electronic state in the tetragonal phase of CaFe2As2
NASA Astrophysics Data System (ADS)
Sakaguchi, Yui; Ikeda, Shugo; Kuse, Tetsuji; Kobayashi, Hisao
2014-07-01
We have investigated the electronic states of single-crystal CaFe2As2 under hydrostatic pressure using 57Fe Mössbauer spectroscopy and magnetization measurements. The center shift and the quadrupole splitting were refined from observed 57Fe Mössbauer spectra using the single-crystalline sample under pressure at room temperature. A discontinuous decrease in the pressure dependence of the refined center shift was observed at 0.33 GPa without any anomaly in the pressure dependence of the refined quadrupole splitting, indicating a purely electronic state change in CaFe2As2 with a tetragonal structure. Such a change is shown to be reflected in the peak-like anomalies observed in the pressure dependences of the magnetic susceptibility at 0.26 GPa above 150 K. Our results reveal that this pressure-induced electronic state change suppresses the tetragonal-to-orthorhombic structural phase transition accompanied by an antiferromagnetic ordering. We further observed superconductivity in CaFe2As2 below ˜8 K around 0.33 GPa although our sample was not in a single phase at this pressure. These findings suggest that the electronic state change observed in CaFe2As2 with the tetragonal structure is relevant to the appearance of the pressure-induced superconductivity in AFe2As2.
NASA Astrophysics Data System (ADS)
Kamiya, Yoshitomo
The possibility of quantum spin liquids, characterized by nontrivial entanglement properties or a topological nonlocal order parameter, has long been debated both theoretically and experimentally. Since candidate systems (e.g., frustrated quantum magnets or 5 d transition metal oxides) may host other competing phases including conventional magnetic ordered phases, it is natural to ask what types of global phase diagrams can be anticipated depending on coupling constants, temperature, dimensionality, etc. In this talk, by considering an extension of the Kitaev toric code Hamiltonians by Ising interactions on 2D (square) and 3D (cubic) lattices, I will present thermodynamic phase diagrams featuring magnetic ``three states of matter,'' namely, quantum spin liquid, paramagnetic, and magnetically ordered phases (analogous to liquid, gas, and solid, respectively, in conventional matter) obtained by unbiased quantum Monte Carlo simulations [YK, Y. Kato, J. Nasu, and Y. Motome, PRB 92, 100403(R) (2015)]. We find that the ordered phase borders on the spin liquid around the exactly solvable point by a discontinuous transition line in 3D, while it grows continuously from the quantum critical point in 2D. In both cases, peculiar proximity effects to the nearby spin liquid phases are observed at high temperature even when the ground state is magnetically ordered. Such proximity effects include flux-shrinking and a tricritical behavior in 3D and a ``fractionalization'' of the order parameter field at the quantum critical point in 2D, both of which can be detected by measuring critical exponents. Work done in collaboration with Yasuyuki Kato, Joji Nasu, and Yukitoshi Motome.
Wang, H L; Yu, X Z; Wang, S L; Chen, L; Zhao, J H
2013-08-01
We have developed a sample rod which makes the conventional superconducting quantum interference device magnetometer capable of performing magnetization and electrical transport measurements simultaneously. The sample holder attached to the end of a 140 cm long sample rod is a nonmagnetic drinking straw or a 1.5 mm wide silicon strip with small magnetic background signal. Ferromagnetic semiconductor (Ga,Mn)As films are used to test the new sample rod, and the results are in good agreement with previous report.
Molecular Quantum Magnetism in LiZn2Mo3O8
NASA Astrophysics Data System (ADS)
Mourigal, Martin
2014-03-01
Considerable theoretical and experimental efforts are devoted to understanding frustrated two-dimensional antiferromagnets, searching for quantum spin-liquid states hosting deconfined fractional spin excitations. To make quantitative comparisons with theory, the sensitivity to defects and site mixing inherent to magnetic transition metal oxides is a significant challenge. Spin degrees of freedom delocalized on stable organic molecules or inorganic clusters offer an interesting alternative. The layered insulating material LiZn2Mo3O8 is such a compound. It comprises spin-1/2 Mo3O13 molecules organized on the triangular lattice. Its thermo-magnetic properties suggest it hosts collective magnetic phenomena with hints of a possible valence-bond condensation and absence of long-range spin order. Inelastic neutron scattering from powder specimen of LiZn2Mo3O8 reveal the presence of gapless collective magnetic excitations at low-energy that are surprisingly broad in momentum space and involve at most a third of the spins. The corresponding structure factor is consistent with the presence of valence-bonds involving nearest-neighbor and next-nearest-neighbor spins. No magnetic signal is apparent at higher energies, suggesting that the remaining spins contribute as a broad continuum rather than as a well defined resonance. LiZn2Mo3O8 thus offers an example of molecular based spin-liquid material with collective excitations consistent with a disordered or dynamic ground-state. Research was supported by the U.S. Department of Energy, office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-FG02-08ER46544.
Why a magnetized quantum wire can act as an optical amplifier: a short survey
NASA Astrophysics Data System (ADS)
Kushwaha, Manvir S.
2014-10-01
This paper reviews the fundamental issues associated with the magnetoplasmon excitations investigated in a semiconducting quantum wire characterized by a harmonic confining potential and subjected to an applied (perpendicular) magnetic field. We embark on the charge-density excitations in a two-subband model within the framework of Bohm-Pines's random-phase approximation. The problem involves two length scales: {l}0 = √ {\\hbar /m*ω0} and {l}c = √ {\\hbar /m*ωc}, which characterize the strengths of the confinement and the magnetic field (B). Essentially, we focus on the device aspects of the intersubband collective (magnetoroton) excitation, which observes a negative group velocity between maxon and roton. Consequently, it leads to tachyon-like (superluminal) behavior without one's having to introduce the negative energies. Existence of the negative group velocity is a clear manifestation of a medium with population inversion brought about due to a metastable state caused by the magnetic field that satisfies the condition B > Bth; Bth being the threshold value below which the magnetoroton does not exist. The interest in negative group velocity is based on anomalous dispersion in a medium with inverted population, so that gain instead of absorption occurs at the frequencies of interest. A medium with an inverted population has the remarkable ability of amplifying a small optical signal of definite wavelength, i.e. it can serve as an active laser medium. An extensive scrutiny of the gain coefficient suggests an interesting and important application: The electronic device designed on the basis of such magnetoroton modes can act as an optical amplifier. Examining the magnetic field dependence of the life-time of magnetorotons leads us to infer that relatively smaller magnetic fields are optimal.
Magnetism in parent Fe-chalcogenides: quantum fluctuations select a plaquette order
NASA Astrophysics Data System (ADS)
Perkins, Natalia; Ducatman, Samuel; Chubukov, Andrey
2013-03-01
The analysis of magnetism in parent compounds of iron-based superconductors (FeSCs) is an integral part of the program to understand the origin of superconductivity in these materials. Here we analyze magnetic order in iron-chalcogenide Fe1+yTe - the parent compound of high-temperature superconductor Fe1+yTe1-xSex. Neutron scattering experiments show that magnetic order in this material contains components with momentum Q1 = (π / 2 , π / 2) and Q2 = (π / 2 , - π / 2) in Fe-only Brillouin zone. The actual spin order depends on the interplay between these two components. Previous works argued that spin order is a single- Q state (either Q1 or Q2). Such an order breaks rotational C4 symmetry and order spins into a double diagonal stripe. We show that quantum fluctuations actually select another order - a double Q plaquette state with equal weight of Q1 and Q2 components, which preserves C4 symmetry but breaks Z4 translational symmetry. We argue that the plaquette state is consistent with recent neutron scattering experiments on Fe1+yTe. supported by the grant NSF-DMR-0844115
Composite quantum spin liquid in a low-dimensional organometallic magnet
Stone, Matthew B; Tian, W.; Lumsden, Mark D; Granroth, Garrett E; Mandrus, David; Chung, J.-H.; Harrison, N.; Nagler, Stephen E
2007-01-01
The quantum magnet dimethylammonium trichlorocuprate (DMACuCl$_3$)has been considered an alternating antiferromagnetic-ferromagnetic (AFM-FM) chain along the $a$-axis, weakly coupled dimers along the $a$-axis and even a collection of isolated FM and AFM dimers. However, no spectroscopic probes have been applied until now to elucidate the underlying nature of the magnetic excitations. We present single crystal inelastic neutron scattering (INS) measurements that clearly indicate the magnetic excitations in DMACuCl$_3$ propagate along the $b$-axis. The spectrum has a gap $\\Delta = 0.95(2)$ meV and bandwidth of $0.71(2)$ meV with excitations characteristic of a quasi-1-dimensional alternating AFM-FM exchange chain. Values of exchange constants place DMACuCl$_3$ in a limit interpolating between coupled AFM $S=\\frac{1}{2}$ dimers and the $S=1$ Haldane chain. In order to consistently describe thermodynamic measurements with our spectroscopic results and the low-temperature crystal structure, we propose a composite two chain model where spin-spin interactions in one of the chains are very weakly correlated.
Magnetic polarons in type-II (Zn,Mn)Se/ZnTe quantum dots
NASA Astrophysics Data System (ADS)
Murphy, J. R.; Barman, B.; Tsai, Y.; Scrace, T.; Pientka, J. M.; Zutic, I.; McCombe, B. D.; Petrou, A.; Cartwright, A. N.; Chou, W. C.; Tsou, M. H.; Yang, C. S.; Sellers, I. R.; Oszwaldowski, R.; Petukhov, A. G.
2014-03-01
We have studied magnetic polaron formation dynamics in (Zn,Mn)Se/ZnTe quantum dots2 (QDs) using time-resolved photoluminescence (TRPL) spectroscopy. The emitted light was spectrally and temporally analyzed; the emission spectra were recorded as function of time delay (Δt) from the exciting laser pulse. The recombination time at T = 10 K in our samples is 2.3 ns. The peak energy of the emission red shifts with increasing Δt due to the lowering of the hole-Mn spin complex (magnetic polaron) energy. From this shift we determined the magnetic polaron formation energy (EMP) at T = 10 K to be 20 meV, which is half the value observed in the ZnSe/(Zn,Mn)Te system studied previously.3EMP decreases with increasing temperature, in contrast to the behavior of the ZnSe/(Zn,Mn)Te system3 in which EMP is temperature independent. These results are discussed in terms of a theoretical model. This work is supported by DOE-BES, ONR and NSF.
Urdampilleta, Matias; Nguyen, Ngoc-Viet; Cleuziou, Jean-Pierre; Klyatskaya, Svetlana; Ruben, Mario; Wernsdorfer, Wolfgang
2011-01-01
We built new hybrid devices consisting of chemical vapor deposition (CVD) grown carbon nanotube (CNT) transistors, decorated with TbPc(2) (Pc = phthalocyanine) rare-earth based single-molecule magnets (SMMs). The drafting was achieved by tailoring supramolecular π-π interactions between CNTs and SMMs. The magnetoresistance hysteresis loop measurements revealed steep steps, which we can relate to the magnetization reversal of individual SMMs. Indeed, we established that the electronic transport properties of these devices depend strongly on the relative magnetization orientations of the grafted SMMs. The SMMs are playing the role of localized spin polarizer and analyzer on the CNT electronic conducting channel. As a result, we measured magneto-resistance ratios up to several hundred percent. We used this spin valve effect to confirm the strong uniaxial anisotropy and the superparamagnetic blocking temperature (T(B) ~ 1 K) of isolated TbPc(2) SMMs. For the first time, the strength of exchange interaction between the different SMMs of the molecular spin valve geometry could be determined. Our results introduce a new design for operable molecular spintronic devices using the quantum effects of individual SMMs.
Modeling of magnetic polaron properties in (Zn,Mn)Te quantum dots
NASA Astrophysics Data System (ADS)
Pientka, James; Barman, B.; Schweidenback, L.; Russ, A. H.; Tsai, Y.; Murphy, J. R.; Cartwright, A. N.; Zutic, I.; McCombe, B. D.; Petrou, A.; Chou, W.-C.; Fan, W. C.; Sellers, I. R.; Petukhov, A. G.; Oszwaldowski, R.
Magnetic polarons in (Zn,Mn)Te quantum dots (QD) show unconventional behavior. These structures exhibit a small red shift of the photoluminescence peak energy in the presence of a magnetic field B and they also have a weak dependence of the polaron energy EMP on temperature T and B. We attribute these properties to a large molecular field Bm that is proportional to the heavy holes spin density. We have calculated Bm using the QD diameter and height as adjustable parameters. Assuming hole localization, this calculation yields values of Bm >20 T. The assumption that the hole localization diameter can be smaller than the QD diameter is justified due to alloy and spin disorder scattering. Using the magnetic polaron free energy, we calculate EMP as function of T and B for a variety of Bm values. To get a weak dependence of EMP on T and Bwe must assume that the polaron temperature is higher than T. This work was supported by U.S. DOE BES, Award DE-SC0004890, NSF DMR-1305770 and U.S. ONR N000141310754.
Urdampilleta, Matias; Nguyen, Ngoc-Viet; Cleuziou, Jean-Pierre; Klyatskaya, Svetlana; Ruben, Mario; Wernsdorfer, Wolfgang
2011-01-01
We built new hybrid devices consisting of chemical vapor deposition (CVD) grown carbon nanotube (CNT) transistors, decorated with TbPc(2) (Pc = phthalocyanine) rare-earth based single-molecule magnets (SMMs). The drafting was achieved by tailoring supramolecular π-π interactions between CNTs and SMMs. The magnetoresistance hysteresis loop measurements revealed steep steps, which we can relate to the magnetization reversal of individual SMMs. Indeed, we established that the electronic transport properties of these devices depend strongly on the relative magnetization orientations of the grafted SMMs. The SMMs are playing the role of localized spin polarizer and analyzer on the CNT electronic conducting channel. As a result, we measured magneto-resistance ratios up to several hundred percent. We used this spin valve effect to confirm the strong uniaxial anisotropy and the superparamagnetic blocking temperature (T(B) ~ 1 K) of isolated TbPc(2) SMMs. For the first time, the strength of exchange interaction between the different SMMs of the molecular spin valve geometry could be determined. Our results introduce a new design for operable molecular spintronic devices using the quantum effects of individual SMMs. PMID:22072910
NASA Astrophysics Data System (ADS)
Yakunin, M. V.; de Visser, Anne; Galistu, Gianni; Podgornykh, S. M.; Sadofyev, Yu G.; Shelushinina, N. G.; Harus, G. I.
2009-02-01
Development of quantum Hall peculiarities due to mobility gap between spin-split magnetic levels with addition of the parallel magnetic field component B|| is analyzed in double quantum wells (DQW) created in InGaAs/GaAs and InAs/AlSb heterosystems chosen due to their relatively large bulk g-factors. In InGaAs/GaAs DQWs, the nonmonotonous behavior of these peculiarities is observed and explained within single-electron approach in terms of competition between enhanced spin splitting and localization of electrons in the layers of DQW with increased B||. In InAs/AlSb DQW, the tunneling connection between the layers is very weak due to high barrier, nevertheless the collective odd-numbered peculiarities are revealed that exist due to spontaneous interlayer phase coherence. B|| destroys these states that is manifested, in particular, in the suppression of the peculiarity for filling factor v = 3.
Magnetic field dependent photoluminescence studies of InGaAs/GaAs strained-single-quantum wells
Jones, E.D.; Dawson, L.R.; Klem, J.F.; Lyo, S.K.; Heiman, D.; Liu, X.C.
1994-08-01
Magnetoluminescence determined conduction-band and valence-band dispersion curves are presented for n-type InGaAs/GaAs stained-single-quantum well structures. The magnetic field range was 0 to 30 tesla, and the temperature varied between 4.2 and 77.4 K.
Falaye, Babatunde James; Sun, Guo-Hua; Silva-Ortigoza, Ramón; Dong, Shi-Hai
2016-05-01
This study presents the confinement influences of Aharonov-Bohm (AB) flux and electric and magnetic fields directed along the z axis and encircled by quantum plasmas on the hydrogen atom. The all-inclusive effects result in a strongly attractive system while the localizations of quantum levels change and the eigenvalues decrease. We find that the combined effect of the fields is stronger than a solitary effect and consequently there is a substantial shift in the bound state energy of the system. We also find that to perpetuate a low-energy medium for the hydrogen atom in quantum plasmas, a strong electric field and weak magnetic field are required, whereas the AB flux field can be used as a regulator. The application of the perturbation technique utilized in this paper is not restricted to plasma physics; it can also be applied in molecular physics.
Falaye, Babatunde James; Sun, Guo-Hua; Silva-Ortigoza, Ramón; Dong, Shi-Hai
2016-05-01
This study presents the confinement influences of Aharonov-Bohm (AB) flux and electric and magnetic fields directed along the z axis and encircled by quantum plasmas on the hydrogen atom. The all-inclusive effects result in a strongly attractive system while the localizations of quantum levels change and the eigenvalues decrease. We find that the combined effect of the fields is stronger than a solitary effect and consequently there is a substantial shift in the bound state energy of the system. We also find that to perpetuate a low-energy medium for the hydrogen atom in quantum plasmas, a strong electric field and weak magnetic field are required, whereas the AB flux field can be used as a regulator. The application of the perturbation technique utilized in this paper is not restricted to plasma physics; it can also be applied in molecular physics. PMID:27300989
Pressure induced metallization of the perovskite Sr{sub 3}Fe{sub 2}O{sub 7}
Rozenberg, G.K.; Machavariani, G.Y.; Pasternak, M.P.; Milner, A.P.; Hearne, G.R.; Taylor, R.D.; Adler, P.
1998-12-31
Electrical, magnetic and structural properties of the antiferromagnetic semiconductor Sr{sub 3}Fe{sub 2}O{sub 7} (Fe{sup 4+}, d{sup 4}) were probed by resistance, Moessbauer spectroscopy (MS) and X-ray diffraction (XRD) measurements to P {approximately} 40 GPa using diamond-anvil cells. A sluggish pressure-induced insulator-metal transition is observed with a clear incipient metallic state at P {ge} 20 GPa. The Fe(IV) 3d magnetic moments remain unaltered across the transition as deduced from MS, and XRD studies show no structural symmetry change to 40 GPa. The results are consistent with carrier delocalization due to p-p gap closure e.g., ligand-to-ligand charge transfer that does not involve the d-states and structural symmetry changes.
Pressure-driven high to low spin transition in the bimetallic quantum magnet [Ru2(O2CMe)4]3[Cr(CN)6
O'Neal, K. R.; Liu, Z.; Miller, Joel S.; Fishman, Randy Scott; Musfeldt, J. L.
2014-01-01
Synchrotron-based infrared and Raman spectroscopies were brought together with diamond anvil cell techniques and an analysis of the magnetic properties to investigate the pressure-induced high low spin transition in [Ru2(O2CMe)4]3[Cr(CN)6]. The extended nature of the diruthenium wavefunction combined with coupling to chromium-related local lattice distortions changes the relative energies of the and orbitals and drives the high low spin transition on the mixed-valence diruthenium complex. This is a rare example of an externally controlled metamagnetic transition in which both spin-orbit and spin-lattice interactions contribute to the mechanism.
Pressure induced structural phase transition in IB transition metal nitrides compounds
NASA Astrophysics Data System (ADS)
Soni, Shubhangi; Kaurav, Netram; Jain, A.; Shah, S.; Choudhary, K. K.
2015-06-01
Transition metal mononitrides are known as refractory compounds, and they have, relatively, high hardness, brittleness, melting point, and superconducting transition temperature, and they also have interesting optical, electronic, catalytic, and magnetic properties. Evolution of structural properties would be an important step towards realizing the potential technological scenario of this material of class. In the present study, an effective interionic interaction potential (EIOP) is developed to investigate the pressure induced phase transitions in IB transition metal nitrides TMN [TM = Cu, Ag, and Au] compounds. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in the EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data.
Bonev, B B; Morrow, M R
1995-01-01
The effects of pressure and temperature on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dimyristoyl-sn-glycero-3-phosphocholine headgroup conformations were examined using deuterium nuclear magnetic resonance. Isothermal compression was found to produce a decrease in the choline alpha deuteron quadrupole splitting and increases in the choline beta and gamma deuteron quadrupole splittings. A similar counterdirectional change, seen in the presence of positive surface charge, has been attributed to tilting of the headgroup away from the bilayer surface in response to the torque exerted on the phosphocholine dipole by positive surface charges. The direction of the change in headgroup deuteron quadrupole splitting is consistent with the pressure-induced reduction in area per lipid in the liquid crystalline phase, which can be inferred from the ordering of phospholipid acyl chains under comparable conditions. The temperature dependences of the headgroup deuteron quadrupole splittings were also examined. It was found that at elevated pressure, the alpha splitting was insensitive to temperature, whereas the beta and gamma splittings decreased. The response of the beta deuteron splitting to temperature was found to be weaker at elevated pressure than at ambient pressure. PMID:8527666
Bonev, B B; Morrow, M R
1995-08-01
The effects of pressure and temperature on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dimyristoyl-sn-glycero-3-phosphocholine headgroup conformations were examined using deuterium nuclear magnetic resonance. Isothermal compression was found to produce a decrease in the choline alpha deuteron quadrupole splitting and increases in the choline beta and gamma deuteron quadrupole splittings. A similar counterdirectional change, seen in the presence of positive surface charge, has been attributed to tilting of the headgroup away from the bilayer surface in response to the torque exerted on the phosphocholine dipole by positive surface charges. The direction of the change in headgroup deuteron quadrupole splitting is consistent with the pressure-induced reduction in area per lipid in the liquid crystalline phase, which can be inferred from the ordering of phospholipid acyl chains under comparable conditions. The temperature dependences of the headgroup deuteron quadrupole splittings were also examined. It was found that at elevated pressure, the alpha splitting was insensitive to temperature, whereas the beta and gamma splittings decreased. The response of the beta deuteron splitting to temperature was found to be weaker at elevated pressure than at ambient pressure. PMID:8527666
Pressure induced structural phase transition in IB transition metal nitrides compounds
Soni, Shubhangi; Kaurav, Netram Jain, A.; Shah, S.; Choudhary, K. K.
2015-06-24
Transition metal mononitrides are known as refractory compounds, and they have, relatively, high hardness, brittleness, melting point, and superconducting transition temperature, and they also have interesting optical, electronic, catalytic, and magnetic properties. Evolution of structural properties would be an important step towards realizing the potential technological scenario of this material of class. In the present study, an effective interionic interaction potential (EIOP) is developed to investigate the pressure induced phase transitions in IB transition metal nitrides TMN [TM = Cu, Ag, and Au] compounds. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in the EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data.
NASA Astrophysics Data System (ADS)
B, Gisi; S, Sakiroglu; İ, Sokmen
2016-01-01
In this work, we investigate the effects of interplay of spin-orbit interaction and in-plane magnetic fields on the electronic structure and spin texturing of parabolically confined quantum wire. Numerical results reveal that the competing effects between Rashba and Dresselhaus spin-orbit interactions and the external magnetic field lead to a complicated energy spectrum. We find that the spin texturing owing to the coupling between subbands can be modified by the strength of spin-orbit couplings as well as the magnitude and the orientation angle of the external magnetic field.
NASA Astrophysics Data System (ADS)
Pervishko, A. A.; Kibis, O. V.; Shelykh, I. A.
2016-08-01
We investigate theoretically the effect of a magnetic field on intersubband polaritons in an asymmetric quantum well placed inside an optical resonator. It is demonstrated that the field-induced diamagnetic shift of electron subbands in the well increases the broadening of optical lines corresponding to intersubband electron transitions. As a consequence, the magnetic field can switch the polariton system from the regime of strong light-matter coupling to the regime of weak one. This effect paves a way to the effective control of polaritonic devices with a magnetic field.
Zhang, Xi; Wang, Chao; Diao, Dongfeng; Sun, Chang Q
2014-07-28
In this paper, we clarified a robust mechanism of magnetism generated by excess electrons captured by edge-quantum well of diamagnetic armchair edges. Consistency between density functional theory calculations and electron cyclotron resonance experiments verified that: (1) Multi-layer armchair nanoribbons are stable with proper amounts of excess electrons which can provide net spin; (2) Since under-coordination induces lattice relaxation and potential well modulation, electrons tend to be trapped at edges; and (3) Neither large amount of excess electrons nor positive charges can induce magnetism. This work shed light on the development of graphene devices in its magnetic applications.
Quantum dots with even number of electrons: kondo effect in a finite magnetic field
Pustilnik; Avishai; Kikoin
2000-02-21
We show that the Kondo effect can be induced by an external magnetic field in quantum dots with an even number of electrons. If the Zeeman energy B is close to the single-particle level spacing Delta in the dot, the scattering of the conduction electrons from the dot is dominated by an anisotropic exchange interaction. A Kondo resonance then occurs despite the fact that B exceeds by far the Kondo temperature T(K). As a result, at low temperatures T
Dąbrowski, M.; Chrapkiewicz, R.; Wasilewski, W.
2016-01-01
Warm atomic vapor quantum memories are simple and robust, yet suffer from a number of parasitic processes which produce excess noise. For operating in a single-photon regime precise filtering of the output light is essential. Here, we report a combination of magnetically tuned absorption and Faraday filters, both light–direction insensitive, which stop the driving lasers and attenuate spurious fluorescence and four-wave mixing while transmitting narrowband Stokes and anti-Stokes photons generated in write-in and readout processes. We characterize both filters with respect to adjustable working parameters. We demonstrate a significant increase in the signal-to-noise ratio upon applying the filters seen qualitatively in measurements of correlation between the Raman scattered photons.
Park, Hoyoung; Lee, Jong-Wook; Hwang, Mintai P; Lee, Kwan Hyi
2013-09-21
Cardiovascular disease (CVD) is a potent cause of mortality in both advanced and developing countries. While soluble CD40L (sCD40L) has been implicated as a correlative factor among CVD patients, methods to quantify sCD40L are not yet well-established. In this paper, we present an ability to separate and quantify sCD40L via a simple immunomagnetic assay. Composed of functionalized magnetic beads conferred with directionality and on-demand detachable quantum dots for subsequent optical analysis, our system utilizes the competitive nature of imidazole and nickel ions for histidine. In essence, we demonstrate the capacity to effectively separate and detect sCD40L within a clinically relevant range that contains the cut-off value for acute coronary disease. While sCD40L was used to conduct this study, we envision the use of our system for the separation and quantification of other biomarkers. PMID:23893124
NASA Astrophysics Data System (ADS)
Dąbrowski, M.; Chrapkiewicz, R.; Wasilewski, W.
2016-11-01
Warm atomic vapor quantum memories are simple and robust, yet suffer from a number of parasitic processes which produce excess noise. For operating in a single-photon regime precise filtering of the output light is essential. Here, we report a combination of magnetically tuned absorption and Faraday filters, both light-direction insensitive, which stop the driving lasers and attenuate spurious fluorescence and four-wave mixing while transmitting narrowband Stokes and anti-Stokes photons generated in write-in and readout processes. We characterize both filters with respect to adjustable working parameters. We demonstrate a significant increase in the signal-to-noise ratio upon applying the filters seen qualitatively in measurements of correlation between the Raman scattered photons.
Nonlinear optics response of semiconductor quantum wells under high magnetic fields
Chemla, D.S.
1993-07-01
Recent investigations on the nonlinear optical response of semiconductor quantum wells in a strong perpendicular magnetic field, H, are reviewed. After some introductory material the evolution of the linear optical properties of GaAs QW`s as a function of H is discussed; an examination is made of how the magneto-excitons (MX) extrapolate continuously between quasi-2D QW excitons (X) when H = 0, and pairs of Landau levels (LL) when H {yields} {infinity}. Next, femtosecond time resolved investigations of their nonlinear optical response are presented; the evolution of MX-MX interactions with increasing H is stressed. Finally, how, as the dimensionality is reduced by application of H, the number of scattering channels is limited and relaxation of electron-hole pairs is affected. How nonlinear optical spectroscopy can be exploited to access the relaxation of angular momentum within magneto-excitons is also discussed.
Itinerancy-enhanced quantum fluctuation of magnetic moments in iron-based superconductors.
Tam, Yu-Ting; Yao, Dao-Xin; Ku, Wei
2015-09-11
We investigate the influence of itinerant carriers on the dynamics and fluctuation of local moments in Fe-based superconductors, via linear spin-wave analysis of a spin-fermion model containing both itinerant and local degrees of freedom. Surprisingly, against the common lore, instead of enhancing the (π,0) order, itinerant carriers with well-nested Fermi surfaces are found to induce a significant amount of spatial and temporal quantum fluctuation that leads to the observed small ordered moment. Interestingly, the underlying mechanism is shown to be an intrapocket nesting-associated long-range coupling rather than the previously believed ferromagnetic double-exchange effect. This challenges the validity of ferromagnetically compensated first-neighbor coupling reported from short-range fitting to the experimental dispersion, which turns out to result instead from the ferro-orbital order that is also found instrumental in stabilizing the magnetic order. PMID:26406850
Quantum Continuum Mechanics for Many-Electron Systems in a Strong Magnetic Field
NASA Astrophysics Data System (ADS)
Pittalis, Stefano; Tokatly, I. V.; Vignale, G.
2011-03-01
A quantum continuum mechanics approach for the determination of the excitation energies of many-electron systems in strong magnetic field is introduced by means of linear response theory (LRT) and time-dependent deformation-functional theory (TD-DefT). In the high-frequency (anti-adiabatic) limit the collective modes of the system appear as the small oscillations of an elastic body in the presence of non-inertial forces reminiscent of the Coriolis and centrifugal forces. Interestingly, the complexity of the problem does not increase significantly with the particle number and only ground state properties are needed as an input. Further results, together with elementary and illustrative examples, may be presented as well. S.P. and G.V. are supported by DOE grant DE-FG02-05ER46203.
Luminescent magnetic quantum dots for in vitro/in vivo imaging and applications in therapeutics.
Acharya, Amitabha
2013-06-01
The quest for design of newer/advanced methods for medical diagnosis and targeted therapeutics are of utmost interest and challenging too, because of its importance in clinical diagnosis. Currently available diagnosis methodologies have their own disadvantages. These shortcomings can be overcome by using multimodal imaging systems where two or more imaging modalities may be coupled. Nanoparticles being widely studied for targeted drug delivery and as biological contrasting agents, might play a decisive role in such findings. This review is focused towards the ongoing research in the area of hybrid nanocomposites which can be used for both as MRI contrasting agent (magnetic nanoparticles) and molecular imaging studies (using fluorescent quantum dots) at in vitro and in vivo level. Though several reports are available in literature for such bimodal imaging systems, their clinical trials are very restricted, possibly because of the lack of communication between the in vitro and in vivo studies. This review is expected to bridge the gap between such studies.
Three-Dimensional Crystallization of Vortex Strings in Frustrated Quantum Magnets.
Wang, Zhentao; Kamiya, Yoshitomo; Nevidomskyy, Andriy H; Batista, Cristian D
2015-09-01
We demonstrate that frustrated exchange interactions can produce exotic 3D crystals of vortex strings near the saturation field (H=H(sat)) of body- and face-centered cubic Mott insulators. The combination of cubic symmetry and frustration leads to a magnon spectrum of the fully polarized spin state (H>H(sat)) with degenerate minima at multiple noncoplanar Q vectors. This spectrum becomes gapless at the quantum critical point H=H(sat) and the magnetic ordering below H(sat) can be formally described as a condensate of a dilute gas of bosons. By expanding in the lattice gas parameter, we find that different vortex crystals span sizable regions of the phase diagrams for isotropic exchange and are further stabilized by symmetric exchange anisotropy. PMID:26382699
Three-Dimensional Crystallization of Vortex Strings in Frustrated Quantum Magnets.
Wang, Zhentao; Kamiya, Yoshitomo; Nevidomskyy, Andriy H; Batista, Cristian D
2015-09-01
We demonstrate that frustrated exchange interactions can produce exotic 3D crystals of vortex strings near the saturation field (H=H(sat)) of body- and face-centered cubic Mott insulators. The combination of cubic symmetry and frustration leads to a magnon spectrum of the fully polarized spin state (H>H(sat)) with degenerate minima at multiple noncoplanar Q vectors. This spectrum becomes gapless at the quantum critical point H=H(sat) and the magnetic ordering below H(sat) can be formally described as a condensate of a dilute gas of bosons. By expanding in the lattice gas parameter, we find that different vortex crystals span sizable regions of the phase diagrams for isotropic exchange and are further stabilized by symmetric exchange anisotropy.
NASA Astrophysics Data System (ADS)
Park, Hoyoung; Lee, Jong-Wook; Hwang, Mintai P.; Lee, Kwan Hyi
2013-08-01
Cardiovascular disease (CVD) is a potent cause of mortality in both advanced and developing countries. While soluble CD40L (sCD40L) has been implicated as a correlative factor among CVD patients, methods to quantify sCD40L are not yet well-established. In this paper, we present an ability to separate and quantify sCD40L via a simple immunomagnetic assay. Composed of functionalized magnetic beads conferred with directionality and on-demand detachable quantum dots for subsequent optical analysis, our system utilizes the competitive nature of imidazole and nickel ions for histidine. In essence, we demonstrate the capacity to effectively separate and detect sCD40L within a clinically relevant range that contains the cut-off value for acute coronary disease. While sCD40L was used to conduct this study, we envision the use of our system for the separation and quantification of other biomarkers.
NASA Astrophysics Data System (ADS)
Sitte, M.; Rosch, A.; Altman, E.; Fritz, L.
2012-03-01
We investigate how a magnetic field induces one-dimensional edge channels when the two-dimensional surface states of three-dimensional topological insulators become gapped. The Hall effect, measured by contacting those channels, remains quantized even in situations where the θ term in the bulk and the associated surface Hall conductivities, σxyS, are not quantized due to the breaking of time-reversal symmetry. The quantization arises as the θ term changes by ±2πn along a loop around n edge channels. Model calculations show how an interplay of orbital and Zeeman effects leads to quantum Hall transitions, where channels get redistributed along the edges of the crystal. The network of edges opens new possibilities to investigate the coupling of edge channels.
Itinerancy enhanced quantum fluctuation of magnetic moments in iron-based superconductors
Tam, Yu -T.; Ku, W.; Yao, D. -X.
2015-09-10
We investigate the influence of itinerant carriers on dynamics and fluctuation of local moments in Fe-based superconductors, via linear spin-wave analysis of a spin-fermion model containing both itinerant and local degrees of freedom. Surprisingly against the common lore, instead of enhancing the (π,0) order, itinerant carriers with well nested Fermi surfaces is found to induce significant amount of spatial and temporal quantum fluctuation that leads to the observed small ordered moment. Interestingly, the underlying mechanism is shown to be intra-pocket nesting-associated long-range coupling, rather than the previously believed ferromagnetic double-exchange effect. This challenges the validity of ferromagnetically compensated first-neighbor coupling reported from short-range fitting to the experimental dispersion, which turns out to result instead from the ferro-orbital order that is also found instrumental in stabilizing the magnetic order.