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Nonreciprocal Charge Transport in an Iron-Based Superconductor with Broken Inversion Symmetry Engineered by a
Takayuki Nagai1, Yukito Nishio1, Jumpei Matsumoto2
1Quantum-Phase Electronics Center (QPEC) and Department of Applied Physics, University of Tokyo, Tokyo, Japan.
Advanced Science (Weinheim, Baden-Wurttemberg, Germany)
|February 15, 2026
Summary
Concentration gradients in solids can break spatial inversion symmetry, leading to unique electronic properties. This study demonstrates nonreciprocal charge transport in a hydrogen-doped superconductor above 40 K due to such a gradient.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Superconductivity
Background:
- Breaking spatial inversion symmetry in materials leads to phenomena like ferroelectricity and nonreciprocal responses.
- Concentration gradients in solids can create quasi-stable nonequilibrium states, potentially breaking inversion symmetry.
Purpose of the Study:
- To propose and demonstrate concentration gradients as a general platform for breaking inversion symmetry in solids.
- To investigate nonreciprocal charge transport in a hydrogen-doped SmFeAsO superconductor with a depthwise hydrogen-concentration gradient.
Main Methods:
- Fabrication of an epitaxial thin film of hydrogen-doped SmFeAsO (Sm1111:H) using a topotactic reaction to introduce a depthwise hydrogen-concentration gradient.
- Measurement of nonreciprocal charge transport (current-direction-dependent resistance) as a signature of broken inversion symmetry.
- Analysis of the nonreciprocal signal's emergence near the superconducting transition and its relation to vortex motion.
Main Results:
- The Sm1111:H thin film with a hydrogen-concentration gradient exhibited nonreciprocal charge transport.
- A significant nonreciprocal signal was observed near the superconducting transition, attributed to vortex-motion nonreciprocity.
- This vortex-origin nonreciprocity was detected above 40 K, the highest reported temperature for single bulk materials without artificial heterostructures.
Conclusions:
- Concentration-gradient engineering is established as a versatile method for inducing inversion symmetry breaking in centrosymmetric materials.
- This approach opens new avenues for realizing materials with odd-parity-driven functionalities.
- The findings highlight the potential of exploiting nonequilibrium states for novel electronic properties in superconductors.
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