Optical Detection Advances Understanding of Wigner Crystals and Valley Pseudospin Orders

The behaviour of electron spin within Wigner crystals, highly ordered states of two-dimensional electrons, presents a long-standing puzzle in condensed matter physics. Yichen Dong, Zhiyuan Sun, and Eugene Demler, working at Tsinghua University and ETH Zurich, now demonstrate a method for both detecting and manipulating these subtle spin arrangements, known as pseudospin orders. Their research reveals that the interplay between electron motion and a property called pseudospin creates unique optical signatures in the terahertz spectrum, allowing scientists to identify different spin orders through light absorption. Importantly, the team also shows that focused light can actively reshape the pseudospin landscape, driving transitions between different ordered states, and opening up possibilities for optical control of these quantum materials. This achievement represents a significant step towards understanding and harnessing the complex magnetic properties of Wigner crystals.

Wigner Crystals and Pseudospin Order Detection

In Wigner-crystal states of two-dimensional electrons, the spin ordering remains poorly understood, due to small energy differences between candidate spin orders and experimental challenges in probing magnetic order at specific wave vectors. This work investigates the optical detection and manipulation of pseudospin orders in Wigner crystals, focusing on the interplay between electron interactions and spin degrees of freedom. The research develops a theoretical framework revealing novel optical signatures of different pseudospin configurations, demonstrating that circularly polarized light can selectively excite collective spin oscillations to identify and control the pseudospin order. Calculations show that the optical absorption spectrum exhibits distinct resonances corresponding to different spin wave modes, with frequencies dependent on the specific pseudospin ordering. Strong light-matter coupling can induce transitions between different pseudospin states, offering a pathway for manipulating the magnetic properties of the Wigner crystal, and highlighting the potential of optical spectroscopy as a powerful tool for investigating correlated electron systems in low-dimensional materials.

Terahertz Spectroscopy Reveals Pseudospin Order in Crystals

Scientists have achieved a breakthrough in understanding and controlling the spin order within Wigner crystals, exotic states of matter formed by electrons interacting strongly at low densities. The study demonstrates a novel method for optically detecting and manipulating pseudospin order, a property arising from valley-related characteristics in modern materials. Researchers harnessed the anomalous velocity arising from valley pseudospin, linking pseudospin texture to electron vibrations, to connect pseudospin texture to electron vibrations, enabling optical detection of these orders. The core of the method involves analyzing terahertz optical conductivity, specifically looking for sharp absorption peaks that signal pseudospin order.

The team demonstrated that antiferromagnetic pseudospin order generates a characteristic absorption peak at the ordering wave vector, resulting from the excitation of collective electronic vibrations, and that a strong optical drive can reshape the pseudospin energy landscape, inducing phase transitions from ferromagnetic to stripe antiferromagnetic states. Measurements confirm that the ordering wave vector of these induced states is tunable by adjusting the frequency of the driving light, offering precise control over the spin configuration. This breakthrough delivers a pathway for optical detection and control of spin order via its coupling to orbital motion, potentially enabling the development of new devices and materials with tailored magnetic properties.

Terahertz Light Controls Pseudospin Order in Crystals

This research establishes a new pathway for both detecting and controlling the ordering of pseudospin in Wigner crystals, unique states of electrons found in two-dimensional materials. Scientists demonstrated that the pseudospin order, arising from the electrons’ motion, influences how they vibrate, creating detectable signals in terahertz light, specifically a characteristic absorption peak in terahertz optical conductivity for antiferromagnetic pseudospin order. Furthermore, the team showed that applying a strong pulse of terahertz light can actively reshape the pseudospin arrangement, inducing transitions to different ordered states, suggesting the possibility of writing and reading stripe antiferromagnetic order with terahertz pulses, potentially leading to advancements in ultrafast data storage.