[Paper Review] Non-Fermi-Liquid Behavior of Superconducting SnH$_4$

I. A. Troyan, Dmitrii V. Semenok+14 more|arXiv (Cornell University)|Mar 11, 2023

Quantum, superfluid, helium dynamics8 citations

TL;DR

The paper reports that superconducting SnH4 under high pressure exhibits non-Fermi-liquid behavior, with deviations from Bloch-Grüneisen scattering and unconventional magnetic-field dependence of superconducting properties. It also quantifies the superconducting gap and critical field behavior.

ABSTRACT

We studied chemical interaction of Sn with H$_2$ by X-ray diffraction methods at pressures of 180-210 GPa. A previously unknown tetrahydride SnH$_4$ with a cubic structure (${fcc}$) exhibiting superconducting properties below ${T}$$_C$ = 72 K was obtained; the formation of a high molecular ${C2/m}$-SnH$_{14}$ superhydride and several lower hydrides, ${fcc}$ SnH$_2$ and ${C2}$-Sn$_{12}$H$_{18}$, was also detected. The temperature dependence of critical current density ${J}$$_C$(T) in SnH$_4$ yields the superconducting gap 2$Δ$(0) = 23 meV at 180 GPa. SnH$_4$ has unusual behavior in strong magnetic fields: ${B,T}$-linear dependences of magnetoresistance and the upper critical magnetic field ${B}$$_{C2}$(T) $\propto$ (${T}$$_C$ - ${T}$). The latter contradicts the Wertheimer-Helfand-Hohenberg model developed for conventional superconductors. Along with this, the temperature dependence of electrical resistance of ${fcc}$ SnH$_4$ in non-superconducting state exhibits a deviation from what is expected for phonon-mediated scattering described by the Bloch-Grüneisen model, and is beyond the framework of the Fermi liquid theory. Such anomalies occur for many superhydrides, making them much closer to cuprates than previously believed.

Motivation & Objective

• Investigate chemical interaction of Sn with H2 under extreme pressure (180–210 GPa) to synthesize SnH4 and related hydrides.
• Characterize the superconducting properties of SnH4, including the superconducting gap and critical fields.
• Examine the temperature and magnetic field dependence of transport and magnetic properties to assess adherence to Fermi-liquid and conventional-superconductor models.
• Identify deviations from standard phonon-mediated scattering and conventional superconductivity theories in SnH4 and related hydrides.

Proposed method

• Perform X-ray diffraction at 180–210 GPa to identify crystal structures and hydride formation.
• Measure temperature dependence of critical current density Jc(T) to extract the superconducting gap via V-I characteristics.
• Determine the superconducting gap from V-I data using the Talantsev–Tallon model.
• Study the temperature dependence of the upper critical field Bc2(T) and magnetoresistance to assess conformity with conventional Werthamer–Helfand–Hohenberg expectations.
• Analyze the normal-state resistance versus temperature to compare with Bloch–Grüneisen and Fermi-liquid expectations.

Experimental results

Research questions

• RQ1 Does SnH4 under high pressure exhibit conventional BCS-like superconductivity or non-Fermi-liquid behavior?
• RQ2 What are the superconducting parameters (gap, Tc, Bc2) of SnH4 at ~180 GPa and how do they evolve with pressure?
• RQ3 How do magnetoresistance, Jc(T), and Bc2(T) deviate from conventional models (Bloch–Grüneisen, WHH) in SnH4?
• RQ4 What is the nature of scattering in the normal state of SnH4, and does it align with Fermi-liquid theory?

Key findings

• SnH4 synthesized at 180–210 GPa shows Tc = 72 K with a superconducting gap 2Δ(0) ≈ 23 meV at 180 GPa.
• Bc2(T) exhibits B,T-linear behavior and follows Bc2(T) ∝ (Tc − T), contradicting Werthamer–Helfand–Hohenberg predictions for conventional superconductors.
• Magnetoresistance shows B-linear dependence in the high-field regime.
• Normal-state resistivity deviates from Bloch–Grüneisen expectations, signaling non-Fermi-liquid behavior beyond standard phonon-mediated scattering.
• The observed anomalies in SnH4 (and related superhydrides) align more closely with cuprate-like behavior rather than conventional superconductors.
• Structural analysis revealed fcc SnH4 and linked higher hydrides (SnH14) and other compositions under the studied pressures.