Recently, SEU Prof. Luo Yue, in collaboration with Harvard University, reported the realization of broadlytunable intersubband polaritons in multilayer van der Waals 

tungsten diselenide (WSe?) quantum wells. By utilizing native-dielectriclayer forhigh-density p-type doping, the research team achieved electrically tunable imaging and 

manipulation of hyperbolic intersubband polaritons in 2D van der Waals quantum wells with varying layer thicknesses. This 2D van der Waals quantum well platform 

holds promise for a wide range of applications in polaritonic devices. This research, titled “Observation of hyperbolic intersubband polaritons in native-dielectric-

doped van der Waals semiconductor quantum wells”, was published in Nature Communications.

In semiconductor quantum wells, electrons are confined tomove within nanoscale spaces, forming a series of discrete energy levels (sub-bands). Transitions between 

these subbands, known as intersubbands transitions, constitute the fundamental physical process underlying key devices such as infrared photodetectors and quantum 

cascade lasers. In recent years, 2D van der Waals materials (e.g., transition metal dichalcogenides, TMDs) have emerged as ideal platforms for constructing quantum 

wells due to their naturally atomically smooth interfaces and stackable properties. However, realizing strongly coupled intersubband polaritons in 2D materials has faced 

significant challenges, primarily due to the mismatch between the optical polarization direction of intersubband transitions and free-space photons, as well as the difficulty 

in achieving sufficiently high carrier densities through conventional electrostatic doping.

The research team proposed an innovative approach: by oxidizing the top layer of multilayer WSe?, a self-limiting transition metal oxide layer is formed. Leveraging the 

work function difference between this oxide layer and the underlying WSe?, efficient charge transfer and ultrahigh-density hole doping (with carrier densities reaching the 

order of 1013 cm?2) were achieved—nearly an order of magnitude higher than that possible with conventional electrostatic doping. This “native dielectric doping” strategy 

not only significantly enhances the oscillator strength of intersubband transitions but also enables direct observation and manipulation of polaritons in multilayer WSe?. 

Using scattering-type scanning near-field optical microscopy (s-SNOM), the team directly observed the propagation behavior of intersubband polaritons in real space with 

nanoscale resolution. In nano-resonators, polaritons were highly localized, forming distinct standing wave patterns with extremely small effective mode volumes, 

demonstrating strong optical field compression capabilities.

This study successfully realized electrically tunable hyperbolic intersubband polaritons in 2D van der Waals quantum wells for the first time. Through modulation of layer 

number, doping, and electric field modulation, the polariton energy can be tuned across the mid-infrared to terahertz frequency range. This method can be extended to 

other TMD material systems, offering new avenues for designing various infrared photonic devices (such as detectors, light sources, and modulators) and providing an 

ideal experimental platform for studying strong light–matter interactions, nonlinear optical effects, and topological photonics.

SEU Prof. Luo Yue is the first and corresponding author, with William L. Wilson, Executive Director of the Center for Nanoscale Systems at Harvard University, serving as 

co-corresponding author. The project was supported by several funding sources, including the Major Research Plan Cultivation Project of the National Natural Science 

Foundation of China and the Southeast University Young Talent Special Support Program.

     Source: School of Electronic Science & Engineering

     Translated by: Melody Zhang

     Proofread by: Gao Min

     Edited by: Li Xinchang