Topology of the Fermi surface beyond the quantum critical point

Khodel, V. A.; Clark, John W.; Zverev, M. V.

doi:10.1103/physrevb.78.075120

Cited by 109 publications

(189 citation statements)

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“…The second derivative must vanish also. Otherwise ε(p) − µ has the same sign below and above the Fermi surface, and the Landau state becomes unstable [2,4]. Zeros of these two subsequent derivatives mean that the spectrum ε(p) has an inflection point at p F so that the lowest term of its p-2 Taylor expansion is proportional to (p − p F ) 3 .…”

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confidence: 99%

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High-magnetic-fields thermodynamics of the heavy-fermion metal YbRh ₂ Si ₂

Shaginyan

Попов

Stephanovich

et al. 2011

EPL

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Abstract. -We perform comprehensive theoretical analysis of high magnetic field behavior of the heavy-fermion (HF) compound YbRh2Si2. At low magnetic fields B, YbRh2Si2 has a quantum critical point related to the suppression of antiferromagnetic ordering at a critical magnetic field B ⊥ c of B = Bc0 ≃ 0.06 T. Our calculations of the thermodynamic properties of YbRh2Si2 in wide magnetic field range from Bc0 ≃ 0.06 T to B ≃ 18 T allow us to straddle a possible metamagnetic transition region and probe the properties of both low-field HF liquid and high-field fully polarized one. Namely, high magnetic fields B ∼ B * ∼ 10 T fully polarize corresponding quasiparticle band generating Landau Fermi liquid (LFL) state and suppressing HF (actually NFL) one, while at elevating temperatures both HF state and corresponding NFL properties are restored. Our calculations are in good agreement with experimental facts and show that the fermion condensation quantum phase transition is indeed responsible for the observed NFL behavior and quasiparticles survive both high temperatures and high magnetic fields.An explanation of the rich and striking behavior of heavy fermion (HF) metals is, as years before, among the main problems of modern condensed matter physics. One of the most interesting and puzzling issues in the research of HF compounds is their non-Fermi liquid (NFL) behavior in a wide range of temperatures T and magnetic fields B. For example, recent measurements of the specific heat C of YbRh 2 Si 2 under the application of magnetic field B show that the above temperature range extends at least up to twenty Kelvins as reported in the inset to fig. 1. As it is well-known from Landau Fermi liquid (LFL) theory, the ratio C/T is proportional to quasiparticle effective mass M * . The inset to fig. 1 reports the dependence of C(T )/T , which has a maximum M * max (B) at some temperature T max (B). It is seen from the inset, that M * max (B) decreases as magnetic field B grows, while T max (B) shifts to higher T reaching 15 K at B = 18 T [1].(a)

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confidence: 99%

“…At high fields, when this dependence is strong and we have full subbands spin polarization, this interpolative solution is no more valid and we should explicitly solve eq. (5) with respect to (3) and (4). It can be shown that magnetic field B enters Landau equation only in combination Bµ B /T making T max ∝ Bµ B [2,5].…”

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confidence: 99%

High-magnetic-fields thermodynamics of the heavy-fermion metal YbRh ₂ Si ₂

Shaginyan

Попов

Stephanovich

et al. 2011

EPL

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“…We note that there are different kinds of instabilities of LFL connected with several perturbations of initial quasiparticle spectrum ε(p) and occupation numbers n(p), associated with strong enhancement of the effective mass and leading to the emergence of a multi-connected Fermi surface, see e.g. [8,[21][22][23]. Depending on the parameters and analytical properties of the Landau interaction, such instabilities lead to several possible types of restructuring of the initial LFL ground state.…”

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confidence: 99%

“…Choice of the interaction and its parameters is dictated by the fact that the system has to be at FCQPT [8,25,26]. Thus, the sole role of the Landau interaction is to bring the system to the FCQPT point, where Fermi surface alters its topology so that the effective mass acquires temperature and field dependence [8,23,25]. The variational procedure, being applied to the functional E[n σ (p, T )], gives the following form for ε σ (p, T ),…”

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Heat transport in magnetic fields by quantum spin liquid in the organic insulators EtMe ₃ Sb[Pd(dmit) ₂ ] ₂ and κ -(BEDT - TTF) ₂ Cu ₂ (CN) ₃

Shaginyan¹,

Msezane²,

Попов³

et al. 2013

EPL

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-Measurements of the low-temperature thermal conductivity collected on insulators with geometrical frustration produce important experimental facts shedding light on the nature of quantum spin liquid composed of spinons. We employ a model of strongly correlated quantum spin liquid located near the fermion condensation phase transition to analyze the exciting measurements of the low-temperature thermal conductivity in magnetic fields collected on the organic insulators EtMe3Sb[Pd(dmit)2]2 and κ − (BEDT − TTF)2Cu2(CN)3. Our analysis of the conductivity allows us to reveal a strong dependence of the effective mass of spinons on magnetic fields, to detect a scaling behavior of the conductivity, and to relate it to both the spin-lattice relaxation rate and the magnetoresistivity. Our calculations and observations are in a good agreement with experimental data.The organic insulators EtMe 3 Sb[Pd(dmit) 2 ] 2 and κ − (BEDT − TTF) 2 Cu 2 (CN) 3 have two-dimensional triangular lattices with the geometric frustration prohibiting the formation of spin ordering even at the lowest accessible temperatures T [1-5]. Therefore, these insulators offer unique insights into the physics of quantum spin liquids (QSL). Indeed, measurements of the heat capacity on the both insulators reveal a T -linear term indicating that the low-energy excitation spectrum from the ground state is gapless [1][2][3]. The excitation spectrum can be deduced from measurements of the heat conductivity κ(T ) in the low temperature regime. For example, at T → 0 a residual value in k/T signals that the excitation spectrum is gapless. The presence of the residual value is clearly resolved in EtMe 3 Sb[Pd(dmit) 2 ] 2 , while measurements of k/T on κ − (BEDT − TTF) 2 Cu 2 (CN) 3 suggests that the low-energy excitation spectrum can have a gap (a) Email: vrshag@thd.pnpi.spb.ru [4,5]. Taking into account the observed T -linear term of the heat capacity in κ − (BEDT − TTF) 2 Cu 2 (CN) 3 with the static spin susceptibility remaining finite down to the lowest measured temperatures [6], the presence of the spin excitation gap becomes questionable. Thermal conductivity probe elementary itinerant excitations and is totally insensitive to localized ones such as those responsible for Schottky contributions, which contaminates the heat capacity measurements at low temperatures [1][2][3][4][5]. The heat conductivity is formed primarily by both acoustic phonons and itinerant spinons, while the latter form QSL. Since the phonon contribution is insensitive to the applied magnetic field B, the elementary excitations of QSL can be further explored by the magnetic field dependence of k. Measurements under the application of magnetic field B of the heat conductivity κ on these insulators have exhibited a strong dependence of κ(B, T ) as a function of B at fixed T [4,5]. The obtained dependence at low temperatures rep-1

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“…Among these QPT's the Lifshitz phase transition (LPT) is marked as a QPT from the fully-gapped state to the state with Fermi surface [12], which should be not confused with the Lifshitz points [13]. In recent years LPT becomes one of the hot topics in condensed matter physics [14][15][16][17]. The LPT in nuclear matter has been studied in Refs.…”

Section: Lifshitz Phase Transitionmentioning

confidence: 99%