Yusuke Iguchi, Ph.D.

Superconductivity and Quantum Materials

I study superconductors and quantum materials through local magnetic measurements and imaging using scanning SQUID microscopy. By spatially resolving magnetic penetration depth, superfluid density, superconducting vortices, and weak magnetic responses, I investigate unconventional and multiband superconductivity, magnetic quantum criticality, and related emergent phenomena.

• Observation of unquantized vortices in the multiband superconductor K$_{0.77}$Ba$_{0.23}$Fe$_2$As$_2$ (Science, 2023).
• Local measurements of superfluid density in UTe$_2$, providing evidence for a homogeneous single superconducting phase at ambient pressure (Physical Review Letters, 2023).
• Observation of anomalous superfluid density in Pd$_x$ErTe$_3$ consistent with strong phase fluctuations described by a quantum rotor model (Physical Review Letters, 2024).
• Real-space imaging of spontaneous magnetism in chiral superconductor candidates (Physical Review B (Letter), 2021; Physical Review B, 2024).
• Identification of magnetic quantum criticality inside the superconducting state of Zn-substituted CeCoIn$_5$ using local $T_c$ and penetration-depth scaling (Physical Review Letters, 2026).

Nonreciprocal Magnonics and Microwave Spectroscopy

During my Ph.D. at the University of Tokyo, I developed cryogenic microwave spectroscopy platforms operating up to 40 GHz and studied nonreciprocal magnon propagation in magnetic materials with broken inversion symmetry.

• Observation of nonreciprocal microwave response arising from asymmetric magnon bands in chiral magnets (Physical Review B, 2015).
• Electrical and magnetic control of microwave nonreciprocity in multiferroic materials (Nature Communications, 2017; Applied Physics Letters, 2022).
• Quantitative observation of nonreciprocal microwave propagation associated with antiferromagnetic magnons (Physical Review B, 2018).

Frustrated Magnetism and Spin-Lattice Coupling

As an undergraduate researcher, I investigated spin-lattice coupling in geometrically frustrated magnets using synchrotron X-ray diffraction under uniaxial pressure. This work revealed an enhanced lattice response near magnetic phase transitions in CuFeO$_2$ (Journal of the Physical Society of Japan, 2013).