Thermodynamic signatures of the field-induced states of graphite

LeBoeuf, David; Rischau, Carl Willem; Seyfarth, Gabriel; Küchler, R.; Berben, Martin; Wiedmann, Steffen; Tabiś, Wojciech; Frachet, M.; Behnia, Kamran; Fauqué, Benoît

doi:10.1038/s41467-017-01394-7

Cited by 20 publications

(25 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The fact that we observe attenuation to increase while σ zz decreases suggests that something other than conventional electronic attenuation is occurring above 80 T in TaAs. The enhanced attenuation could come from the interaction between ultrasound and order-parameter fluctuations, as it does in graphite where it peaks near each field-induced phase transition 46 . The unbounded growth in attenuation we observe suggests that either we have not yet reached the attenuation peak, or that a different attenuation mechanism is at work.…”

Section: Resultsmentioning

confidence: 99%

Quantum limit transport and destruction of the Weyl nodes in TaAs

et al. 2018

View full text Add to dashboard Cite

Weyl fermions are a recently discovered ingredient for correlated states of electronic matter. A key difficulty has been that real materials also contain non-Weyl quasiparticles, and disentangling the experimental signatures has proven challenging. Here we use magnetic fields up to 95 T to drive the Weyl semimetal TaAs far into its quantum limit, where only the purely chiral 0th Landau levels of the Weyl fermions are occupied. We find the electrical resistivity to be nearly independent of magnetic field up to 50 T: unusual for conventional metals but consistent with the chiral anomaly for Weyl fermions. Above 50 T we observe a two-order-of-magnitude increase in resistivity, indicating that a gap opens in the chiral Landau levels. Above 80 T we observe strong ultrasonic attenuation below 2 K, suggesting a mesoscopically textured state of matter. These results point the way to inducing new correlated states of matter in the quantum limit of Weyl semimetals.

show abstract

Section: Resultsmentioning

confidence: 99%

Quantum limit transport and destruction of the Weyl nodes in TaAs

et al. 2018

View full text Add to dashboard Cite

show abstract

“…This leads to the field-temperature phase diagram of Fig.2 (c). The phase A and B were known previously [12,13]. In all three phases, the temperature dependence of ρ xx remains metallic.…”

mentioning

confidence: 97%

Graphite in 90 T: Evidence for Strong-Coupling Excitonic Pairing

et al. 2019

View full text Add to dashboard Cite

Strong magnetic field induces at least two phase transitions in graphite beyond the quantum limit where many-body effects are expected. We report on a study using a state-of-the-art nondestructive magnet allowing to attain 90.5 T at 1.4 K, which reveals a new field-induced phase and evidence that the insulating state destroyed at 75 T is an excitonic condensate of electron-hole pairs. By monitoring the angle dependence of in-plane and out-of-plane magnetoresistance, we distinguish between the role of cyclotron and Zeeman energies in driving various phase transitions. We find that, with the notable exception of the transition field separating the two insulating states, the threshold magnetic field for all other transitions display an exact cosine angular dependence. Remarkably, the threshold field for the destruction of the second insulator (phase B) is temperature-independent with no detectable Landau-level crossing nearby. We conclude that the field-induced insulator starts as a weak-coupling spin-density-wave, but ends as a strong-coupling excitonic insulator of spin-polarized electron-hole pairs.

show abstract

“…Above the quantum limit of 7.4 T, electrons and holes are both confined to their lowest Landau levels (23,24), which are each split to two spin-polarized subbands. A rich phase diagram consisting of distinct fieldinduced phases emerges above ∼20 T, which was documented by previous studies (25)(26)(27)(28). Our focus, here, is the identification of the peak transition temperature as the cradle of the excitonic instability.…”

mentioning

confidence: 52%

Critical point for Bose–Einstein condensation of excitons in graphite

Wang

Nie

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

An exciton is an electron–hole pair bound by attractive Coulomb interaction. Short-lived excitons have been detected by a variety of experimental probes in numerous contexts. An excitonic insulator, a collective state of such excitons, has been more elusive. Here, thanks to Nernst measurements in pulsed magnetic fields, we show that in graphite there is a critical temperature (T = 9.2 K) and a critical magnetic field (B = 47 T) for Bose–Einstein condensation of excitons. At this critical field, hole and electron Landau subbands simultaneously cross the Fermi level and allow exciton formation. By quantifying the effective mass and the spatial separation of the excitons in the basal plane, we show that the degeneracy temperature of the excitonic fluid corresponds to this critical temperature. This identification would explain why the field-induced transition observed in graphite is not a universal feature of three-dimensional electron systems pushed beyond the quantum limit.

show abstract

Thermodynamic signatures of the field-induced states of graphite

Cited by 20 publications

References 36 publications

Quantum limit transport and destruction of the Weyl nodes in TaAs

Quantum limit transport and destruction of the Weyl nodes in TaAs

Graphite in 90 T: Evidence for Strong-Coupling Excitonic Pairing

Critical point for Bose–Einstein condensation of excitons in graphite

Contact Info

Product

Resources

About