Nernst Response of the Landau Tubes in Graphite across the Quantum Limit

Abstract

We report on a study of the Nernst effect in graphite extended up to 45 T. The Nernst response sharply peaks when a Landau tube is squeezed inside the thermally fuzzy Fermi surface and presents a temperature-independent fixed point when the tube flattens to a single ring. Beyond the quantum limit, the onset of the field-induced phase transition leads to a drastic drop in the Nernst response signaling the sudden vanishing of Landau tubes. The magnitude of this drop suggests the destruction of multiple Landau tubes possibly as a result of simultaneous nesting of the electron and hole pockets.PACS numbers: 71.70. Di, 72.15.Gd Manifestations of electron-electron interaction in graphene are a current subject of intense attention [1][2][3]. Meanwhile, in a macroscopic stack of graphene layers, a phase transition induced by strong magnetic field was discovered three decades ago [4,5] and is believed to be driven by Coulomb interaction [6]. A large magnetic field applied perpendicular to the conducting planes of graphite confines both electrons and holes of the semimetal to their lowest Landau levels. A variety of instabilities can occur in a three-dimensional electron gas in such a context [7]. A Charge-Density-Wave (CDW) transition resulting from the 2k F nesting is the one which was proposed by Yoshioka and Fukuyama(YF)[8] to explain the field-induced phase transition in graphite. This scenario and its variants remain the one most commonly invoked to explain this transition.The magnitude of the field necessary to induce the transition (≥ 25 T) is beyond what can be obtained by commercially available magnets. Therefore, experimental studies of this transition have been scarce and limited to resistivity measurements [9][10][11][12][13][14][15]. They have uncovered the destruction of the field-induced state at still higher fields [12]. The existence of such a reentrant transition, believed to occur when an additional Landau sub-level is depopulated, is in agreement with the YF scenario. The magnitude of the reentrant field (∼ 53 T) implies significant many-body corrections to the single-particle spectrum [16]. On the other hand, a number of experimental findings do not easily fit the YF picture. Observation of nonlinear in-plane conductivity implies a CDW vector with an in-plane component, in contrast to what is expected in the simplest nesting scenario [17]. Moreover, the structure of the phase transition appears to be complex with several transitions giving rise to different signatures in the in-plane and out-of-plane charge transport [14,15].Recent experimental studies [18,19] have found that the Nernst effect is a sensitive probe of the threedimensional electron gas in the vicinity of the quantum limit. According to a recent theoretical investigation [20] the van Hove singularity in the density of states at the intersection of a Landau level and a Fermi level leads to a particularly sharp peak in the transverse thermoelectric response. Fundamentally, since the Nernst response monitors the density of states per ca...

Nernst effect in metals and superconductors: a review of concepts and experiments

“…In both systems, a field of 10 T suffices to attain the quantum limit. During the last few years, unexpectedly large oscillations of the Nernst response was reported in both bismuth [84] and graphite [21,85] in the vicinity of the quantum limit. In both these systems, when a few Landau tubes remain, a large oscillatory Nernst response dominates the monotonous background.…”

Two Phase Transitions Induced by a Magnetic Field in Graphite

“…In the early eighties, a phase transition in this system was discovered by Tanuma and co-workers who reported a sharp increase in the in-plane magnetoresistance of graphite at B≈25 T [8]. Numerous experimental studies followed [9][10][11][12][13][14][15] and confirmed the existence of a field-induced many-body state beyond a temperature-dependent critical magnetic field. Soon after the initial experimental discovery, Yoshioka and Fukuyama (YF) [16] ascribed this instability to a charge-density-wave (CDW).…”

Wide Critical Fluctuations of the Field-Induced Phase Transition in Graphite

“…The present result helps to understand the evolution of the observed anomalies in the Nernst effect [12,29] (a measure of the entropy per carrier [30]) and the ultrasound measurements [13] caused by the transition. At low temperature, one expects that ordering induces a smooth variation in entropy (see [17]) and therefore a rounded drop in the Nernst response [12,29]. As the temperature increases the mean field component of the transition strengthens and the Nernst anomaly becomes a clear kink.…”

“…In the early 80s Tanuma and co-workers [5] discovered the onset of an electronic phase transition at B=25T and T=1.3K. Since then, extensive electrical [6][7][8][9][10][11], thermo-electrical [12] and ultrasound measurements [13] at high magnetic field have established that graphite hosts a succession of, at least, two field induced phases [7,11] arising from electron-hole instabilities. Depending on the nesting vector considered and the strength of the electron-electron interaction, various types of charge [10,14], spin [15] density waves or an excitonic insulating phase [8,9,11,16] have been proposed.…”