Dongbin Shin

The Josephson junction (JJ) is the fundamental nonlinear building block of superconducting quantum technologies. Its macroscopic quantum tunneling physics underpins superconducting quantum computing, sensing, and communication, but scaling these platforms to utility‐scale architectures places increasingly stringent demands on junction materials, interfaces, and fabrication. Practical quantum computing requires high reproducibility, low power consumption, tunability, a small device footprint, and resilience to noise and defects. This review surveys how advances in materials science, device characterization, and nanofabrication are addressing these challenges and redefining the figures of merit for next‐generation JJs. This review also examines the evolution of fabrication strategies, from conventional multi‐angle evaporation to foundry‐compatible superconducting processes and the integration of emerging junction materials. Progress along these directions will determine how rapidly JJs move from laboratory‐scale components to the foundation of industrial‐scale quantum processors.

Chiral‐lattice degrees of freedom can offer novel chirality‐selective functionalities for thermotronic applications. Chiral phonons, which carry both heat and angular momentum, can arise from broken chiral degeneracy in phonon bands or from angular momentum transfer from photons or spins. Here, we demonstrate a nanoscale chirality‐selective phonon transport based on a simple heterostructure of ferromagnetic [Co/Pt] multilayers and insulating chiral α‐SiO ₂ . Using magneto‐optic thermometry, we show that the effective thermal conductivity of α‐SiO ₂ depends systematically on both the magnetization direction of [Co/Pt] and the structural handedness of α‐SiO ₂ . This behavior is supported by first‐principles‐based molecular dynamics simulations, which reveal chirality‐dependent phonon transport across the ferromagnet/chiral‐material interface. The magnetization‐dependent thermal on/off ratio reaches 1.07 at room temperature and increases to approximately 1.2 at 50 K, reflecting reduced Umklapp phonon–phonon scattering. These results establish a ferromagnet/chiral‐material platform for controlling nanoscale heat flow through chiral phonons.

Light-induced symmetry breaking offers a powerful route to manipulate material properties by driving them into non-equilibrium states. Here, we demonstrate that a linearly polarized light transiently breaks time-reversal symmetry in bilayer MoSe₂, a nominally non-magnetic van der Waals system. Combined ultrafast measurements and first-principles simulations reveal that linearly polarized excitation launches interlayer-coupled coherent phonons through a displacive mechanism. Time-resolved Faraday rotation measurements confirm that the excitation of two coherent phonons by a linearly polarized light is responsible for breaking time-reversal symmetry. Remarkably, the subsequent beating between the interlayer breathing mode and the in-plane Se-stretching mode, together with asymmetric charge redistribution, phonon dissipation, and spin-layer locking, generates an effective oscillating magnetization. Our findings uncover a new light-induced pathway for interlayer phonon coupling, revealing hidden non-equilibrium functionalities of van der Waals crystals. Our results establish a foundation for light-controlled functionality in stacked two-dimensional systems, advancing the emerging paradigm of materials-on-demand.

Strong light-matter interactions can be exploited to modify properties of quantum materials both in and out of thermal equilibrium. Recent studies suggest that electromagnetic fields in photonic structures can hybridize with condensed matter systems, resulting in photon field–dressed collective quantum. Here, we show that photon fields in photonic structures, including optical cavities and waveguides, induce emergent topological phases in solids through polarization-mediated symmetry-breaking mechanisms. Using state-of-the-art quantum electrodynamic density functional theory calculations, we demonstrate that strong light-matter coupling can reconfigure both the electronic and ionic structures of HgTe, driving the system into Weyl, nodal-line, or topological insulator phases. These phases depend on the relative orientation of the sample in the coupling strength. In contrast with laser-driven phenomena, the photon field–induced symmetry breaking arises from steady-state photon-matter hybridization, enabling multiple robust topological states to emerge. Our study demonstrates that vacuum fluctuations in photonic structures can be used to engineer material properties and realize rich topological phenomena in quantum materials on demand.

Recent studies of organic molecular solids have focused on their complex phase diagram and on light-induced phenomena, including a Mott insulating state, a spin liquid phase, and light-enhanced superconductivity. However, discrepancies between experiments and first-principles calculations for the κ -(BEDT-TTF) ₂ X family hinder a comprehensive understanding of their properties. Here, we revisit the electronic structure of κ -(BEDT-TTF) ₂ Cu ₂ (CN) ₃ with a recently developed method for applying the Hubbard U potential on generalized orbital states, within the framework of density functional theory, to correct the orbital energy levels of the molecular solid. Our work focuses on the electronic structure of κ -(BEDT-TTF) ₂ Cu ₂ (CN) ₃ , whose insulating state originates from an energy gap between the highest occupied and the lowest unoccupied molecular orbital states of the BEDT-TTF dimers, which constitute the periodic unit of the molecular solid. Our calculations provide results in alignment with experiments for band gaps, optical conductivities, and evolution of the metal-insulator transition as a function of pressure. Especially, the observed superconducting dome of κ -(BEDT-TTF) ₂ Cu ₂ (CN) ₃ , which derives from the flat band state at the Fermi level, is qualitatively reproduced. Additionally, we construct a new low-energy lattice model based on our first-principles computed band structure that can be exploited to address many-body physics, such as quantum spin liquid states and double-holon dynamics. Our work can be extended to achieve deeper insight into the complex phase diagram and light-induced phenomena in the κ -(BEDT-TTF) ₂ X family and other complex organic molecular solids.

Understanding nonadiabatic carrier-lattice interactions at the atomic scale remains a fundamental challenge, yet these processes govern energy transfer in materials and ultimately set limits in microelectronics. We combined attosecond core-level transient absorption spectroscopy with many-body theory to uncover how nonadiabatic electron-phonon coupling drives ultrafast relaxations in a titanium-carbide MXene. Phonon-driven changes in carrier localization modulated local field effects (LFEs), yielding carrier-, site-, and orbital-specific absorption signatures. LFEs served as sensitive fingerprints of electron-phonon coupling strength across the phonon spectrum and revealed a breakdown of the Born–Oppenheimer approximation: Electrons lagged lattice oscillations by 32 ± 8 femtoseconds, whereas holes responded almost instantaneously (7 ± 7 femtoseconds). Our results establish a framework for probing and controlling nonadiabatic carrier-phonon interactions with orbital and site specificity.

Chiral-lattice degrees of freedom can offer novel chirality-selective functionalities for thermotronic applications. Chiral phonons, carrying both heat and angular momentum, can emerge through a breaking of chiral degeneracy in the phonon bands, either via an intrinsic chiral crystal structure or by angular momentum transfer from photons or spins. This chiral controllability of the lattice dynamics enables a design of chiral thermo-devices by integrating ferromagnets with chiral materials. Here, we present a nanoscale chirality-selective thermal switch realized using a simple heterostructure composed of ferromagnetic [Co/Pt] multilayers and insulating chiral $α$-SiO2, where an external magnetic field can control thermal transport properties. Our experimental results based on the magneto-optic thermometry reveal that the thermal conductivity of $α$-SiO2 exhibits a clear dependence on both the magnetization direction of [Co/Pt] multilayers and the structural chirality of $α$-SiO2, which is supported well by the first-principles-based molecular dynamic simulations. The magnetization-dependent thermal on/off ratio amounts to 1.07 at room temperature and increases to about 1.2 as temperature decreases to 50 K, due to a reduction of Umklapp phonon-phonon scattering rate in $α$-SiO2. These findings provide the first experimental demonstration of the nanoscale chirality-selective thermal switch based on the ferromagnetic/chiral material heterostructure, highlighting its potential as a key technology for addressing heat dissipation challenges in nanoscale electronic devices.

Structuring the photon density of states and light-matter coupling in optical cavities has emerged as a promising approach to modifying the equilibrium properties of materials through strong light-matter interactions. In this article, we employ state-of-the-art quantum electrodynamical density functional theory (QEDFT) to study the modifications of the electronic and structural properties of two-dimensional (2D) van der Waals (vdW) layered materials by the cavity vacuum field fluctuations. We find that cavity photons modify the electronic density through localization along the photon polarization directions, a universal effect observed for all the 2D materials studied here. This modification of the electronic structure tunes the material properties, such as the shifting of energy valleys in monolayer h-BN and 2H-MoS$_2$, enabling tunable band gaps. Also, it tunes the interlayer spacing in bilayer 2H-MoS$_2$ and T$_\text{d}$-MoTe$_2$, allowing for adjustable ferroelectric, nonlinear Hall effect, and optical properties, as a function of light-matter coupling strength. Our findings open an avenue for engineering a broad range of 2D layered quantum materials by tuning vdW interactions through fluctuating cavity photon fields.

Strong light-matter interactions can be exploited to modify properties of quantum materials both in and out of thermal equilibrium. Recent studies suggest electromagnetic fields in photonic structures can hybridize with condensed matter systems, resulting in photon field-dressed collective quantum states such as charge density waves, superconductivity, and ferroelectricity. Here, we show that photon fields in photonic structures, including optical cavities and waveguides, induce emergent topological phases in solids through polarization-mediated symmetry-breaking mechanisms. Using state-of-the-art quantum electrodynamic density functional theory (QEDFT) calculations, we demonstrate that strong light-matter coupling can reconfigure both the electronic and ionic structures of HgTe, driving the system into Weyl, nodal-line, or topological insulator phases. These phases depend on the relative orientation of the sample in the photonic structures, as well as the coupling strength. Unlike previously reported laser-driven phenomena with ultrashort lifetimes, the photon field-induced symmetry breaking arises from steady-state photon-matter hybridization, enabling multiple robust topological states to emerge. Our study demonstrates that vacuum fluctuations in photonic structures can be used to engineer material properties and realize rich topological phenomena in quantum materials on demand.

The recent rise in interest in altermagnetism─a magnetic state distinct from ferromagnetism and antiferromagnetism─nessitates the development of a reliable probing method to distinguish it from other types of compensated magnetism. Here, we investigate nonrelativistic spin groups and relativistic magnetic groups to identify and categorize the permissible spin and charge photocurrents of compensated collinear magnets. Our results indicate that, in altermagnets, the charge and spin photocurrents exhibit a similar temperature profile due to their shared dependence on carrier relaxation effects, whereas in antiferromagnets, these currents behave in stark contrast. As a real-material example, we performed first-principles calculations of the altermagnetic phase of MnO and analyzed it using a simplified four-band model. We demonstrate that the normal injection current directly reflects the magnetic band geometry of altermagnets: the direction and magnitude of the injection current are delicately correlated with the interband Berry curvature and the alternating spin splitting of energy bands. We suggest that nonlinear photocurrent could serve as a promising probing tool to reveal the particular magnetic phase and band geometry of altermagnets.