洞見 - Condensed Matter Physics - # Superconductivity and Charge Density Wave in NbTe2

Significant Enhancement of Superconductivity Coexisting with Charge Density Wave in Lattice-Expanded NbTe2

Q: How do the different growth conditions affect the stabilization of specific CDW phases in NbTe2, and how are these phases related to the observed enhancement of superconductivity?

The growth conditions of NbTe2 significantly influence the stabilization of specific charge density wave (CDW) phases due to variations in temperature gradients and the presence of different precursors during the synthesis process. In the study, the authors noted that the Tc-enhanced NbTe2 sample was synthesized by skipping the polycrystal growth step, which likely altered the temperature profile during crystal growth. This change could lead to the stabilization of different CDW phases, such as the peculiar long-period CDW (√19 × √19) known as the David star, which is associated with Mott phases. The relationship between these CDW phases and the observed enhancement of superconductivity (from 0.56 K to 2.8 K) is complex. Typically, CDW formation can suppress superconductivity by opening an energy gap that reduces the available Fermi surface for Cooper pair formation. However, in the case of NbTe2, the coexistence of CDW and enhanced superconductivity suggests a more cooperative interaction. The specific CDW phase stabilized under the altered growth conditions may facilitate a unique electronic environment that supports superconductivity, possibly by allowing for enhanced electron-phonon coupling or by maintaining a portion of the Fermi surface that is conducive to pairing despite the presence of the CDW.

Q: What are the potential mechanisms that allow the coexistence of enhanced superconductivity and CDW order in NbTe2, in contrast to the typical competition observed in other TMD superconductors?

The coexistence of enhanced superconductivity and CDW order in NbTe2, as opposed to the typical competition seen in other transition metal dichalcogenides (TMDs), can be attributed to several potential mechanisms. First, the study indicates that the unit cell expansion (~1%) in the Tc-enhanced sample does not significantly alter the density of states (DOS) at the Fermi level, which is often a critical factor in superconductivity. This suggests that the electronic structure remains favorable for superconductivity even in the presence of CDW. Moreover, the authors propose that the CDW in NbTe2 may not merely suppress superconductivity but could instead play a role in enhancing it. The CDW fluctuations might provide a medium for Cooper pairing, allowing for a unique interplay between the two orders. This is in contrast to other TMD superconductors, where the suppression of CDW typically leads to a significant increase in Tc. The structural characteristics of NbTe2, including the preservation of the distorted 1T” structure and the presence of multi-domain formations, may also contribute to this coexistence by maintaining a favorable electronic environment that supports both orders.

Q: Could the presence of multiple CDW phases in the Tc-enhanced NbTe2 sample be related to the emergence of topologically nontrivial electronic states, and how might this influence the superconducting properties?

Yes, the presence of multiple CDW phases in the Tc-enhanced NbTe2 sample could indeed be related to the emergence of topologically nontrivial electronic states. Theoretical predictions and experimental observations suggest that NbTe2 possesses topologically nontrivial bands, which can be confirmed by phenomena such as linear magnetoresistance at high magnetic fields. The stabilization of different CDW phases may influence the topology of the electronic states, potentially leading to a richer electronic structure that supports superconductivity. The interplay between CDW phases and topologically nontrivial states could enhance the superconducting properties by providing additional channels for electron pairing. For instance, the unique band structure associated with topological states may allow for enhanced electron-phonon coupling or facilitate the formation of Cooper pairs in a manner that is not typically observed in conventional superconductors. This relationship underscores the complexity of the electronic interactions in NbTe2 and suggests that the coexistence of CDW and superconductivity may be a manifestation of underlying topological phenomena, which could be further explored through advanced techniques such as scanning tunneling microscopy (STM) to directly observe the spatial distribution of superconducting gaps and CDW order.

核心概念

The superconducting transition temperature (Tc) of NbTe2 is significantly enhanced from 0.56 K to 2.8 K, while the charge density wave (CDW) order still coexists in the lattice-expanded sample.

摘要

The authors report a large enhancement of the superconducting transition temperature (Tc) in the transition metal dichalcogenide (TMD) material NbTe2, from 0.56 K to 2.8 K. Detailed structural analysis reveals that the Tc-enhanced sample has an anisotropic lattice distortion, leading to a ~1% expansion of the unit cell volume, while maintaining the 1T" structure closely related to the CDW order.

Despite the unit cell expansion, Hall measurements show that the electronic structure does not change significantly between the standard and Tc-enhanced samples, suggesting that the CDW order still coexists with the enhanced superconductivity. This is unlike the behavior observed in other TMD superconductors, where the suppression of CDW typically leads to a large Tc enhancement.

The first-principles calculations indicate that the unit cell volume expansion does not result in a significant increase in the density of states at the Fermi level, ruling out this as the origin of the Tc enhancement. The authors propose that the growth conditions may lead to the stabilization of different types of CDW phases in the Tc-enhanced sample, which could be related to the observed Tc enhancement. Further microscopic investigations, such as scanning tunneling microscopy, are suggested to unveil the underlying mechanism.

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統計資料

The Tc-enhanced sample shows a critical magnetic field (Hc2(0)) of ~2.5 T, which is vastly enhanced compared to 0.04 T for the standard sample.
The residual resistance ratio (RRR) of the Tc-enhanced sample is ~1, while the standard sample has an RRR of 5-6, indicating more disorder in the Tc-enhanced sample.
The superconducting volume fraction of the Tc-enhanced sample is estimated to be 0.025%.

引述

"The Tc-enhanced sample has the onset temperature at 2.8 K which is 5 times higher than that of the standard sample (Tc = 0.56 K)."
"Despite the unit cell expansion, the distorted 1T structure, closely related to the charge density wave (CDW) order in this material, persists."
"These results suggest that the CDW still coexists with the enhanced superconductivity unlike the other TMD superconductors."

從以下內容提煉的關鍵洞見

Enhancement of superconductivity coexisting with charge density wave in lattice expanded $\textrm{NbTe}_2$

by Takaya Shimo... 於 arxiv.org 10-03-2024

https://arxiv.org/pdf/2410.01247.pdf

$Enhancement of superconductivity coexisting with charge density wave in lattice expanded $\textrm{NbTe}_2$$

深入探究

How do the different growth conditions affect the stabilization of specific CDW phases in NbTe2, and how are these phases related to the observed enhancement of superconductivity?

The growth conditions of NbTe2 significantly influence the stabilization of specific charge density wave (CDW) phases due to variations in temperature gradients and the presence of different precursors during the synthesis process. In the study, the authors noted that the Tc-enhanced NbTe2 sample was synthesized by skipping the polycrystal growth step, which likely altered the temperature profile during crystal growth. This change could lead to the stabilization of different CDW phases, such as the peculiar long-period CDW (√19 × √19) known as the David star, which is associated with Mott phases.
The relationship between these CDW phases and the observed enhancement of superconductivity (from 0.56 K to 2.8 K) is complex. Typically, CDW formation can suppress superconductivity by opening an energy gap that reduces the available Fermi surface for Cooper pair formation. However, in the case of NbTe2, the coexistence of CDW and enhanced superconductivity suggests a more cooperative interaction. The specific CDW phase stabilized under the altered growth conditions may facilitate a unique electronic environment that supports superconductivity, possibly by allowing for enhanced electron-phonon coupling or by maintaining a portion of the Fermi surface that is conducive to pairing despite the presence of the CDW.

What are the potential mechanisms that allow the coexistence of enhanced superconductivity and CDW order in NbTe2, in contrast to the typical competition observed in other TMD superconductors?

The coexistence of enhanced superconductivity and CDW order in NbTe2, as opposed to the typical competition seen in other transition metal dichalcogenides (TMDs), can be attributed to several potential mechanisms. First, the study indicates that the unit cell expansion (~1%) in the Tc-enhanced sample does not significantly alter the density of states (DOS) at the Fermi level, which is often a critical factor in superconductivity. This suggests that the electronic structure remains favorable for superconductivity even in the presence of CDW.
Moreover, the authors propose that the CDW in NbTe2 may not merely suppress superconductivity but could instead play a role in enhancing it. The CDW fluctuations might provide a medium for Cooper pairing, allowing for a unique interplay between the two orders. This is in contrast to other TMD superconductors, where the suppression of CDW typically leads to a significant increase in Tc. The structural characteristics of NbTe2, including the preservation of the distorted 1T” structure and the presence of multi-domain formations, may also contribute to this coexistence by maintaining a favorable electronic environment that supports both orders.

Could the presence of multiple CDW phases in the Tc-enhanced NbTe2 sample be related to the emergence of topologically nontrivial electronic states, and how might this influence the superconducting properties?

Yes, the presence of multiple CDW phases in the Tc-enhanced NbTe2 sample could indeed be related to the emergence of topologically nontrivial electronic states. Theoretical predictions and experimental observations suggest that NbTe2 possesses topologically nontrivial bands, which can be confirmed by phenomena such as linear magnetoresistance at high magnetic fields. The stabilization of different CDW phases may influence the topology of the electronic states, potentially leading to a richer electronic structure that supports superconductivity.
The interplay between CDW phases and topologically nontrivial states could enhance the superconducting properties by providing additional channels for electron pairing. For instance, the unique band structure associated with topological states may allow for enhanced electron-phonon coupling or facilitate the formation of Cooper pairs in a manner that is not typically observed in conventional superconductors. This relationship underscores the complexity of the electronic interactions in NbTe2 and suggests that the coexistence of CDW and superconductivity may be a manifestation of underlying topological phenomena, which could be further explored through advanced techniques such as scanning tunneling microscopy (STM) to directly observe the spatial distribution of superconducting gaps and CDW order.