# Spontaneous Magnetic Field near a Time-Reversal Symmetry Broken Surface State of YBCO

## TL;DR

This paper calculates the distribution of spontaneous magnetic fields near the surface of YBCO superconductors with broken time-reversal symmetry using Ginzburg-Landau theory, highlighting their confined nature and potential for experimental detection.

## Contribution

It introduces a theoretical framework for predicting spontaneous magnetic fields near YBCO surfaces with broken time-reversal symmetry based on the $t-J$ model and Ginzburg-Landau theory.

## Key findings

- Magnetic fields are confined within a narrow region inside the superconductor.
- Magnetic fields decay rapidly outside the surface.
- Potential experimental methods for detection are discussed.

## Abstract

Spatial distributions of spontaneous magnetic fields near a surface of cuprate high-$T_C$ superconductor YBCO with broken time-reversal symmetry are calculated using the Ginzburg-Landau theory derived from the $t-J$ model. It is found that the magnetic field exists in a narrow region inside the superconductor, and it decays quickly outside the surface. Experimental approaches possible to detect such spontaneous magnetic fields are discussed.