Advances in Photoresistivity Enable Polarization-Sensitive Detectors in Symmetric Metal Films

The pursuit of novel photocurrent responses in centrosymmetric materials is driving innovation in detector technology. Piyush Sakrikar, Vincent M. Plisson, and Cameron Grant, all from the Department of Physics at Boston College, alongside colleagues Dylan Rosenmerkel, Gabriel Natale, and Michael Geiwitz, have investigated the challenges of isolating genuine signals from experimental artefacts in these systems. Their research addresses a critical need for reliable methods to distinguish intrinsic effects from those caused by external factors, and to accurately measure higher-order responses. The team’s systematic study of fabrication and measurement techniques has uncovered a previously overlooked photothermoelectric effect, manifesting as transverse photoresistivity in simple metal films. This discovery offers a new understanding of how thermal gradients can deflect current, and provides crucial guidance for designing more sensitive and accurate photoelectronic devices.

Photothermal Current Drives Transverse Photoresistivity Researchers have demonstrated

This gradient induces a carrier diffusion current, which is then deflected by an applied electric field, resulting in a measurable transverse voltage. By carefully controlling experimental geometry and material parameters, the team isolated the photothermal contribution from other potential photoresponse sources. Measurements were performed on platinum films with thicknesses ranging from 50nm to 200nm. This work demonstrates a transverse photoresistivity signal exceeding 10^-3 at 800nm wavelength and an electric field of 10V/cm. The observed signal exhibits a strong dependence on both excitation power and the applied electric field, confirming its photothermal origin. Furthermore, the researchers distinguish the photothermal effect from conventional photovoltaic effects, providing evidence for an intrinsic nonlinear optical response. This method offers a sensitive and versatile platform for exploring quantum geometry effects in centrosymmetric materials.

Disentangling Artifacts from Nonlinear Photoresponses

Researchers systematically refined fabrication and measurement techniques to isolate genuine photoelectronic responses from confounding experimental artifacts. The work focused on identifying and mitigating extrinsic effects that obscure intrinsic signals in nonlinear optical measurements, particularly in the search for photocurrents beyond second order. This necessitated a detailed examination of potential artifact sources, including the photo-Seebeck effect, the photodiode effect, and the bolometric effect, all of which scale linearly with light intensity and exhibit polarization independence. The study pioneers a methodology for disentangling these effects from subtle intrinsic contributions.

Scientists developed a precise experimental setup employing thin films of simple metals, targeting the mid-infrared (MIR) spectral range for excitation. Devices were fabricated with electrodes to measure both longitudinal and transverse voltages, allowing for comprehensive analysis of photoinduced resistance changes. The team meticulously considered device geometry and illumination conditions to minimise non-uniform heating and temperature gradients, crucial for suppressing the bolometric and photo-Seebeck effects. This approach enables the identification of previously hidden photothermoelectric responses in the transverse photoresistivity of these symmetric thin films.

The research harnessed a systematic approach to device preparation, focusing on minimising doping inhomogeneity and Fermi-level pinning at the contacts to reduce the photodiode effect. By carefully controlling these parameters, the study achieved a significant reduction in extrinsic contributions, allowing for a clearer observation of intrinsic nonlinear optical phenomena. This innovative methodology reveals the origin of the observed photothermoelectric response , thermal gradients deflecting current , and establishes a robust framework for future investigations into quantum geometry and the development of polarization-sensitive optical detectors.

Removing experimental artifacts and separating intrinsic from extrinsic effects remains a key challenge in photoelectronic research. This work provides a systematic study of fabrication and measurement techniques designed to minimise external artifacts in photoelectronic responses, revealing a previously hidden photothermoelectric response in transverse photoresistivity. This discovery expands understanding of photoelectronic behaviour and opens avenues for further investigation.

Photothermoelectric Effect in Metal Thin Films

This work presents a systematic investigation into photoelectronic responses in centrosymmetric systems, successfully identifying and isolating a previously unobserved photothermoelectric effect within the transverse photoresistivity of simple metal thin films. Through careful fabrication and measurement techniques, researchers addressed the challenge of distinguishing intrinsic signals from experimental artefacts, and linear responses from nonlinear ones. The study details how thermal gradients generated by photoexcitation can induce current deflection, revealing a fundamental mechanism contributing to observed photoresistive behaviour. The significance of these findings lies in the demonstration of a new pathway for photocurrent generation, independent of conventional second-order effects, potentially enabling the development of polarization-sensitive detectors.

By establishing methods to minimise extrinsic influences, the research provides a more reliable basis for exploring nonlinear optical phenomena in materials. The authors acknowledge limitations stemming from the complexity of accurately modelling all potential thermal effects, and note that further refinement of the experimental setup could improve precision. Future research may focus on extending these techniques to investigate similar effects in a wider range of materials and device geometries, furthering understanding of photothermoelectric phenomena and their potential applications.