اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدMajoranas in mixed-valence insulators
71
0
0.0
(
0
)
تأليف
C.M. Varma
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
A physical model for a mixed-valence impurity in a metal must satisfy the Friedel screening theorem for both valences. Such a model is shown, following earlier work which showed low energy singularities in it, to be supersymmetric, leading to a free Majorana and a phase-shifted Majorana excitation. The theory extended approximately to a lattice of mixed-valence ions at appropriate filling gives, without fine-tuning the parameters, a protected gapless Majorana fermion band across the chemical potential, besides the mixed-valence particle and hole bands separated by gaps. In this situation the system is electrically neutral in linear response but has de Haas-van Alphen oscillations. This is used to explain the recently observed magneto-oscillations in mixed-valence insulators as well as their accompanying low energy thermodynamic and relaxation rate anomalies. Some predictions to test the validity of the theoretical results are provided, the most striking of which is that there should be extensive ground state entropy in such compounds.
قيم البحث
اقرأ أيضاً
Possible topological nature of Kondo and mixed valence insulators has been a recent topic of interest in condensed matter physics. Attention has focused on SmB6, which has long been known to exhibit low temperature transport anomaly, whose origin is
of independent interest. We argue that it is possible to resolve the topological nature of surface states by uniquely accessing the surface electronic structure of the low temperature anomalous transport regime through combining state-of-the-art laser- and synchrotron-based angle-resolved photoemission spectroscopy (ARPES) with or without spin resolution. A combination of low temperature and ultra-high resolution (laser) which is lacking in previous ARPES studies of this compound is the key to resolve the possible existence of topological surface state in SmB6. Here we outline an experimental algorithm to systematically explore the topological versus trivial or mixed (topological and trivial surface state admixture as in the first 3D TI Bi$_{1-x}$Sb$_x$) nature of the surface states in Kondo and mixed valence insulators. We conclude based on this methodology that the observed topology of the surface Fermi surface in our low temperature data considered within the level of current resolution is consistent with the theoretically predicted topological picture, suggesting a topological origin of the dominant in-gap ARPES signal in SmB6.}
Interacting many-body systems combining confined and extended dimensions, such as ladders and few layer systems are characterized by enhanced quantum fluctuations, which often result in interesting collective properties. Recently two-dimensional bila
yer systems, such as twisted bilayer graphene or ultracold atoms, have sparked a lot of interest because they can host rich phase diagrams, including unconventional superconductivity. Here we present a theoretical proposal for realizing high temperature pairing of fermions in a class of bilayer Hubbard models. We introduce a general, highly efficient pairing mechanism for mobile dopants in antiferromagnetic Mott insulators, which leads to binding energies proportional to $t^{1/3}$, where $t$ is the hopping amplitude of the charge carriers. The pairing is caused by the energy that one charge gains when retracing a string of frustrated bonds created by another charge. Concretely, we show that this mechanism leads to the formation of highly mobile, but tightly bound pairs in the case of mixed-dimensional Fermi-Hubbard bilayer systems. This setting is closely related to the Fermi-Hubbard model believed to capture the physics of copper oxides, and can be realized by currently available ultracold atom experiments.
The low-temperature electron spin resonance (ESR) spectra and the static magnetization data obtained for the stoichiometric single crystals of $beta$-Na$_{0.33}$V$_2$O$_5$ indicate that this quasi-one-dimensional mixed valence (V4+/V5+) compound demo
nstrates at $T_N=22$ K the phase transition into the canted antiferromagnetically ordered state. The spontaneous magnetization of $3.4times 10^{-3}$ $mu_B$ per V$^{4+}$ ion was found to be oriented along the two-fold $b$ axis of the monoclinic structure, the vector of antiferromagnetism is aligned with the $a$ axis and the Dzyaloshinsky vector is parallel to the $c$-axis. The experimental data were successfully described in the frame of the macroscopic spin dynamics and the following values for the macroscopic parameters of the spin system were obtained: the Dzyaloshinsky field $H_D=6$ kOe, the energy gaps of two branches of the spin wave spectrum $Delta_1=48$ GHz and $Delta_2=24$ GHz.
Quantum criticality has been considered to be specific to crystalline materials such as heavy fermions. Very recently, however, the Tsai-type quasicrystal Au51Al34Yb15 has been reported to show unusual quantum critical behavior. To obtain a deeper un
derstanding of this new material, we have searched for other Tsai-type cluster materials. Here, we report that the metal alloys Au44Ga41Yb15 and Ag47Ga38Yb15 are members of the 1/1 approximant to the Tsai-type quasicrystal and that both possess no localized magnetic moment. We suggest that the Au-Al-Yb system is located near the border of the divalent and trivalent states of the Yb ion; we also discuss a possible origin of the disappearance of magnetism, associated with the valence change, by the substitution of the constituent elements.
Fermi liquid theory, the standard theory of metals, has been challenged by a number of observations of anomalous metallic behavior found in the vicinity of a quantum phase transition. The breakdown of the Fermi liquid is accomplished by fine-tuning t
he material to a quantum critical point using a control parameter such as the magnetic field, pressure, or chemical composition. Our high precision magnetization measurements of the ultrapure f-electron based superconductor {beta}-YbAlB4 demonstrate a scaling of its free energy indicative of zero-field quantum criticality without tuning in a metal. The breakdown of Fermi-liquid behavior takes place in a mixed-valence state, in sharp contrast with other known examples of quantum critical f-electron systems that are magnetic Kondo lattice systems with integral valence.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
