Continuous phase transitions and critical points, often crucial for revealing exotic states of matter in condensed matter physics, are characterized by critical behavior such as divergent susceptibilities, long-range correlations, and fluctuations that span from kHz to GHz. In this work, we employ scanning nitrogen-vacancy (NV) center-based magnetometry and relaxometry to probe the critical behavior of a high-Tc ferromagnetic oxide near its Curie temperature. Our findings capture both the static and dynamic aspects of critical behavior, offering insights into the universal properties governing phase transitions in magnetic materials. 

Y.-C. Wu, et al. Nano Lett., 25, 1473–1479 (2025)

The moiré superlattices of twisted bilayers have drawn significant attention recently with remarkable findings of the Mott insulator and generalized Wigner crystal states in the system. We report highly tunable valley polarization of interlayer excitons subjected to moiré potential and correlated phases with electrical, optical, and magnetic field tuning.

Y.-C. Wu et al. Physical Review Letters 134 (25), 256402 (2025)

Monolayer TMDs hold potential for valleytronics due to their band structure and spin-orbital coupling. We reported counterintuitive scattering-enhanced valley polarization of excitons. The precession of the exciton's valley pseudospin is disrupted by scatterings with charges (doping) and phonons (temperature), leading to the preserved valley polarization. 

 Y.-C. Wu et al., Physical Review B, 104, L121408 (2021)

We report the observation of light-induced exciton-polaron energy splitting in monolayer WSe2 without a magnetic field. The energy splitting and circular polarization from the exciton-polaron's emission can be attributed to optical-induced valley-polarized carriers. The result paves the way for optical-addressable spin-current in quantum materials. 

Y.-C. Wu, T. Taniguchi, K. Watanabe, and J. Yan, ACS Nano, 17, 15641–15647 (2023)

We report efficient stimuli to dark exciton (spin-1 exciton) in 2D semiconductor materials using the TM mode (out-of-plane electrical field) of SiNx waveguides. The energetic up- and down-conversion from the long-live excitons to other exciton species are demonstrated when the optical excitation is tuned in resonance with the dark exciton. 

Y.-C. Wu, S. Samudrala, A. McClung, T. Taniguchi, K. Watanabe, A. Arbabi and J. Yan, ACS Nano, 14, 10503 (2020)

A long-lasting conductivity enhancement of monolayer MoS2 phototransistors upon light illumination is reported in this work. We attributed the mechanism to extrinsic random potential fluctuation from interfacing with SiO2 substrates.  A much-improved photocurrent response time with suspended devices is demonstrated.

  Y.-C. Wu, C.-H. Liu, S.-Y. Chen, F.-Y. Shih, P.-H. Ho, C.-W. Chen, C.-T. Liang, and W.-H. Wang,  Scientific Reports, 5, 11472 (2015)

The thickness-dependent bandgap and electrical tunable Fermi level of 2D materials provide a tunable energy gap across few-layer/few-layer junctions. We reported the photovoltaic of the homojunction and the tuning of Voc and Isc with gate voltage, optical power, and different environmentally controlled conditions.

F.-Y. Shih, Y.-C. Wu, Y.-S. Shih, M.-C. Shih, T.-S. Wu, P.-H. Ho, C.-W. Chen, Y.-F. Chen, Y.-P. Chiu, W.-H. Wang,  Scientific Reports, 7, 44678 (2017)  

The study of coherent phonon transport at the nanoscale is essential to understand heat transfer and mechanical properties at the nanoscale. We reported an efficient generation and detection of acoustic phonon modes propagating in GaAs nanorods with two-color pump-probe techniques. The deposited Au nanodisks are transducers, launching vibrations into nanorods by initial pump-induced thermal expansion. The optical detection of acoustic phonons is achieved by probing the localized plasmon resonance of the nanodisks.

 S.-C. Yang, Y.-C. Wu, P.-A. Mante , C.-C. Chen, H.-P. Chen , H.-Y. Chou , M.-H. Shih, C.-K. Sun,  Applied Physics Letters, 105, 243101 (2014)

The nanowire superlattices are excellent detectors of acoustic phonons at specific frequencies, allowing the observation of the strong dispersion of guided acoustic phonons as a result of nanoconfinement. The generation of high-frequency coherent guided acoustic phonons could be useful to realize an acoustic transducer with a nano lateral size and as a source to understand the thermal behavior of nanowires. 

P.-A. Mante, Y.-C. Wu, Y.-T. Lin, C.-Y. Ho, L.-W. Tu, and C.-K. Sun, Nano Letters, 13, 1139 (2013).

We used ultrafast pump-probe techniques to probe the confined acoustic vibration of nanostructures. The experiment result was compared with the theoretical vibration spectrum, allowing us to extract geometry-dependent elastic constants of the nanostructures.

H.-P. Chen, Y.-C. Wu, P.-A. Mante, S.-J. Tu, J.-K. Sheu and C.-K. Sun, Optics Express, 20, 16611 (2012)