Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Chiral Anomaly and Ultrahigh Mobility in Crystalline HfTe5
77
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
HfTe5 is predicted to be a promising platform for studying topological phases. Here through an electrical transport study, we present the first observation of chiral anomaly and ultrahigh mobility in HfTe5 crystals. Negative magneto-resistivity in HfTe5 is observed when the external magnetic and electrical fields are parallel (B//E) and quickly disappears once B deviates from the direction of E. Quantitative fitting further confirms the chiral anomaly as the underlying physics. Moreover, by analyzing the conductivity tensors of longitudinal and Hall traces, ultrahigh mobility and ultralow carrier density are revealed in HfTe5, which paves the way for potential electronic applications.
rate research
Read More
There is a long-standing confusion concerning the physical origin of the anomalous resistivity peak in transition metal pentatelluride HfTe5. Several mechanisms, like the formation of charge density wave or polaron, have been proposed, but so far no conclusive evidence has been presented. In this work, we investigate the unusual temperature dependence of magneto-transport properties in HfTe5. We find that a three dimensional topological Dirac semimetal state emerges only at around Tp (at which the resistivity shows a pronounced peak), as manifested by a large negative magnetoresistance. This accidental Dirac semimetal state mediates the topological quantum phase transition between the two distinct weak and strong topological insulator phases in HfTe5. Our work not only provides the first evidence of a temperature-induced critical topological phase transition in HfTe5, but also gives a reasonable explanation on the long-lasting question.
Resistivity anomaly, a sharp peak of resistivity at finite temperatures, in the transition-metal pentatellurides ZrTe5 and HfTe5 was observed four decades ago, and more exotic and anomalous behaviors of electric and thermoelectric transport were revealed recent years. Here we present a theory of Dirac polarons, composed by massive Dirac electrons and holes in an encircling cloud of lattice displacements or phonons at finite temperatures. The chemical potential of Dirac polarons sweeps the band gap of the topological band structure by increasing the temperature, leading to the resistivity anomaly. Formation of a nearly neutral state of Dirac polarons accounts for the anomalous behaviors of the electric and thermoelectric resistivity.
Based on first-principles calculations and symmetry-based indicator analysis, we find a class of topological crystalline insulators (TCIs) with $C_2$ rotation anomaly in a family of Zintl compounds, including $mathrm{Ba}_{3}mathrm{Cd}_{2}mathrm{As}_{4}$, $mathrm{Ba}_{3}mathrm{Zn}_{2}mathrm{As}_{4}$ and $mathrm{Ba}_{3}mathrm{Cd}_{2}mathrm{Sb}_{4}$. The nontrivial band topology protected by coexistence of $C_2$ rotation symmetry and time-reversal symmetry $T$ leads to two surface Dirac cones at generic momenta on both top and bottom surfaces perpendicular to the rotation axis. In addition, ($d-2$)-dimensional helical hinge states are also protected along the hinge formed by two side surfaces parallel with the rotation axis. We develop a method based on Wilson loop technique to prove the existence of these surface Dirac cones due to $C_2$ anomaly and precisely locate them as demonstrated in studying these TCIs. The helical hinge states are also calculated. Finally, we show that external strain can be used to tune topological phase transitions among TCIs, strong Z$_2$ topological insulators and trivial insulators.
Topological crystalline insulators (TCIs) possess metallic surface states protected by crystalline symmetry, which are a versatile platform for exploring topological phenomena and potential applications. However, progress in this field has been hindered by the challenge to probe optical and transport properties of the surface states owing to the presence of bulk carriers. Here we report infrared (IR) reflectance measurements of a TCI, (001) oriented $Pb_{1-x}Sn_{x}Se$ in zero and high magnetic fields. We demonstrate that the far-IR conductivity is unexpectedly dominated by the surface states as a result of their unique band structure and the consequent small IR penetration depth. Moreover, our experiments yield a surface mobility of 40000 $cm^{2}/(Vs)$, which is one of the highest reported values in topological materials, suggesting the viability of surface-dominated conduction in thin TCI crystals. These findings pave the way for exploring many exotic transport and optical phenomena and applications predicted for TCIs.
Topological crystalline insulators (TCIs) are insulating electronic states with nontrivial topology protected by crystalline symmetries. Recently, theory has proposed new classes of TCIs protected by rotation symmetries ^C$_n$, which have surface rotation anomaly evading the fermion doubling theorem, i.e. n instead of 2n Dirac cones on the surface preserving the rotation symmetry. Here, we report the first realization of the ^C$_2$ rotation anomaly in a binary compound SrPb. Our first-principles calculations reveal two massless Dirac fermions protected by the combination of time-reversal symmetry ^T and ^C$_{2y}$ on the (010) surface. Using angle-resolved photoemission spectroscopy, we identify two Dirac surface states inside the bulk band gap of SrPb, confirming the ^C$_2$ rotation anomaly in the new classes of TCIs. The findings enrich the classification of topological phases, which pave the way for exploring exotic behaviour of the new classes of TCIs.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
