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The study of thermoelectric behaviors in miniatured transistors is of fundamental importance for developing bottom-level thermal management. Recent experimental progress in nanothermetry has enabled studies of the microscopic temperature profiles of nanostructured metals, semiconductors, two-dimensional material, and molecular junctions. However, observations of thermoelectric (such as nonequilibrium Peltier and Thomson) effect in prevailing silicon (Si)—a critical step for on-chip refrigeration using Si itself—have not been addressed so far. Here, we carry out nanothermometric imaging of both electron temperature ( T e ) and lattice temperature ( T L ) of a Si nanoconstriction device and find obvious thermoelectric effect in the vicinity of the electron hotspots: When the electrical current passes through the nanoconstriction channel generating electron hotspots (with T e ~1500 K being much higher than T L ~320 K), prominent thermoelectric effect is directly visualized attributable to the extremely large electron temperature gradient (~1 K/nm). The quantitative measurement shows a distinctive third-power dependence of the observed thermoelectric on the electrical current, which is consistent with the theoretically predicted nonequilibrium thermoelectric effects. Our work suggests that the nonequilibrium hot carriers may be potentially utilized for enhancing the thermoelectric performance and therefore sheds new light on the nanoscale thermal management of post-Moore nanoelectronics. Thermoelectric property of silicon itself is important for the thermal management of post-Moore nanoelectronics. Here, Xue et al directly observe unconventional thermoelectric cooling/heating effects enhanced by hot electrons in silicon nanodevices.

Broken symmetries play a fundamental role in superconductivity and influence many of its properties in a profound way. Understanding these symmetry breaking states is essential to elucidate the various exotic quantum behaviors in non-trivial superconductors. Here, we report an experimental observation of spontaneous rotational symmetry breaking of superconductivity at the heterointerface of amorphous (a)-YAlO 3 /KTaO 3 (111) with a superconducting transition temperature of 1.86 K. Both the magnetoresistance and superconducting critical field in an in-plane field manifest striking twofold symmetric oscillations deep inside the superconducting state, whereas the anisotropy vanishes in the normal state, demonstrating that it is an intrinsic property of the superconducting phase. We attribute this behavior to the mixed-parity superconducting state, which is an admixture of s -wave and p -wave pairing components induced by strong spin-orbit coupling inherent to inversion symmetry breaking at the heterointerface of a-YAlO 3 /KTaO 3 . Our work suggests an unconventional nature of the underlying pairing interaction in the KTaO 3 heterointerface superconductors, and brings a new broad of perspective on understanding non-trivial superconducting properties at the artificial heterointerfaces. Superconducting interfaces involving KTaO3 have recently attracted attention due to their relatively high transition temperature. Here, the authors study amorphous-YAlO 3 /KTaO 3 interfaces and find two-fold symmetry in the superconducting regime, possibly due to a mixed-parity superconducting state.

Heat dissipation is one of the most serious problems in modern integrated electronics with the continuously decreasing devices size. Large portion of the consumed power is inevitably dissipated in the form of waste heat which not only restricts the device energy-efficiency performance itself, but also leads to severe environment problems and energy crisis. Thermoelectric Seebeck effect is a green energy-recycling method, while thermoelectric Peltier effect can be employed for heat management by actively cooling overheated devices, where passive cooling by heat conduction is not sufficiently enough. However, the technological applications of thermoelectricity are limited so far by their very low conversion efficiencies and lack of deep understanding of thermoelectricity in microscopic levels. Probing and managing the thermoelectricity is therefore fundamentally important particularly in nanoscale. In this short review, we will first briefly introduce the microscopic techniques for studying nanoscale thermoelectricity, focusing mainly on scanning thermal microscopy (SThM). SThM is a powerful tool for mapping the lattice heat with nanometer spatial resolution and hence detecting the nanoscale thermal transport and dissipation processes. Then we will review recent experiments utilizing these techniques to investigate thermoelectricity in various nanomaterial systems including both (two-material) heterojunctions and (single-material) homojunctions with tailored Seebeck coefficients, and also spin Seebeck and Peltier effects in magnetic materials. Next, we will provide a perspective on the promising applications of our recently developed Scanning Noise Microscope (SNoiM) for directly probing the non-equilibrium transporting hot charges (instead of lattice heat) in thermoelectric devices. SNoiM together with SThM are expected to be able to provide more complete and comprehensive understanding to the microscopic mechanisms in thermoelectrics. Finally, we make a conclusion and outlook on the future development of microscopic studies in thermoelectrics.

Optical sensors with in-cell logic and memory capabilities offer new horizons in realizing machine vision beyond von Neumann architectures and have been attempted with two-dimensional materials, memristive oxides, phase-changing materials etc. Noting the unparalleled performance of superconductors with both quantum-limited optical sensitivities and ultra-wide spectrum coverage, here we report a superconducting memlogic long-wave infrared sensor based on the bistability in hysteretic superconductor-normal phase transition. Driven cooperatively by electrical and optical pulses, the device offers deterministic in-sensor switching between resistive and superconducting (hence dissipationless) states with persistence > 105 s. This results in a resilient reconfigurable memlogic system applicable for, e.g., encrypted communications. Besides, a high infrared sensitivity at 12.2 μm is achieved through its in-situ metamaterial perfect absorber design. Our work opens the avenue to realize all-in-one superconducting memlogic sensors, surpassing biological retina capabilities in both sensitivity and wavelength, and presents a groundbreaking opportunity to integrate visional perception capabilities into superconductor-based intelligent quantum machines.We demonstrate a novel superconducting LWIR sensor integrating the function of infrared sensitivity, memory and reconfigurable logic computing.

Majorana fermions have been observed in topological insulator/s-wave superconductor heterostructures. To manipulate Majorana fermions, superconducting materials should be deposited on the surfaces of topological insulators. In this study, highquality superconducting PdTe 2 films are deposited on the topological insulator Bi 2 Te 3 surface using molecular beam epitaxy. The surface topography and electronic properties of PdTe 2 /Bi 2 Te 3 heterostructures are investigated via in situ scanning tunneling microscopy/spectroscopy. Under Te-rich conditions, the Pd atoms presumably form PdTe 2 film on Bi 2 Te 3 surface rather than diffuse into Bi 2 Te 3 . The superconductivity of the PdTe 2 /Bi 2 Te 3 heterostructure is detected at a transition temperature of ~1.4 K using the two-coil mutual inductance technique. This study proposes a method for fabricating superconducting materials on topological insulator surfaces at low doping levels, paving ways for designing nanodevices that can manipulate Majorana fermions.

Majorana fermions have been observed in topological insulator/s-wave superconductor heterostructures. To manipulate Majorana fermions, superconducting materials should be deposited on the surfaces of topological insulators. In this study, highquality superconducting Pd[Te.sub.2] films are deposited on the topological insulator [Bi.sub.2][Te.sub.3] surface using molecular beam epitaxy. The surface topography and electronic properties of Pd[Te.sub.2]/[Bi.sub.2][Te.sub.3] heterostructures are investigated via in situ scanning tunneling microscopy/spectroscopy. Under Te-rich conditions, the Pd atoms presumably form Pd[Te.sub.2] film on [Bi.sub.2][Te.sub.3] surface rather than diffuse into [Bi.sub.2][Te.sub.3]. The superconductivity of the Pd[Te.sub.2]/[Bi.sub.2][Te.sub.3] heterostructure is detected at a transition temperature of ~1.4 K using the two-coil mutual inductance technique. This study proposes a method for fabricating superconducting materials on topological insulator surfaces at low doping levels, paving ways for designing nanodevices that can manipulate Majorana fermions. topological insulator, superconductor, heterostructure, molecular beam epitaxy PACS number(s): 68.37.Ef, 68.55.-a, 73.20.-r, 74.78.-w

Broken symmetries play a fundamental role in superconductivity and influence many of its properties in a profound way. Understanding these symmetry breaking states is essential to elucidate the various exotic quantum behaviors in non-trivial superconductors. Here, we report an experimental observation of spontaneous rotational symmetry breaking of superconductivity at the heterointerface of amorphous (a)-YAlO /KTaO (111) with a superconducting transition temperature of 1.86 K. Both the magnetoresistance and superconducting critical field in an in-plane field manifest striking twofold symmetric oscillations deep inside the superconducting state, whereas the anisotropy vanishes in the normal state, demonstrating that it is an intrinsic property of the superconducting phase. We attribute this behavior to the mixed-parity superconducting state, which is an admixture of s-wave and p-wave pairing components induced by strong spin-orbit coupling inherent to inversion symmetry breaking at the heterointerface of a-YAlO /KTaO . Our work suggests an unconventional nature of the underlying pairing interaction in the KTaO heterointerface superconductors, and brings a new broad of perspective on understanding non-trivial superconducting properties at the artificial heterointerfaces.

The emergence of quantum metallic state marked by a saturating finite electrical resistance in the zero-temperature limit in a variety of two-dimensional superconductors injects an exciting momentum to the realm of heterostructure superconductivity. Despite much research efforts over last few decades, there is not yet a general consensus on the nature of this unexpected quantum metal. Here, we report the observation of a unique quantum metallic state within the hallmark of Bose-metal in the titanium sesquioxide heterointerface superconductor Ti\\(_2\\)O\\(_3\\)/GaN. Remarkably, the quantum bosonic metallic state continuously tuned by a magnetic field in the vicinity of the two-dimensional superconductivity-metal transition persists in the normal phase, indicating the existence of composite bosons formed by electron Cooper pairs even in the normal phase. Our findings provide a distinct evidence for electron pairing in the normal phase of heterointerface superconductors, and shed fresh light on the pairing nature underlying heterointerface superconductivity.

The charge frustration with the mixed-valence state inherent to LiTi\\(_2\\)O\\(_4\\), which is found to be a unique spinel oxide superconductor, is the impetus for paying special attention to reveal the existence of intriguing superconducting properties. Here, we report a pronounced fourfold rotational symmetry of the superconductivity in high-quality single-crystalline LiTi\\(_2\\)O\\(_4\\) (001) thin films. Both the magnetoresistivity and upper critical field under an applied magnetic field manifest striking fourfold oscillations deep inside the superconducting state, whereas the anisotropy vanishes in the normal state, demonstrating that it is an intrinsic property of the superconducting phase. We attribute this behavior to the unconventional \\(d\\)-wave superconducting Cooper pairs with the irreducible representation of \\(E_g\\) protected by \\(O_h\\) point group in LiTi\\(_2\\)O\\(_4\\). Our findings demonstrate the unconventional character of the pairing interaction in a three-dimensional spinel oxide superconductor and shed new light on the pairing mechanism of unconventional superconductivity.

The study of exotic superconductivity in two dimensions has been a central theme in solid state and materials research communities. Experimentally exploring and identifying new fascinating interface superconductors with a high transition temperature (\\(T_c\\)) is challenging. Here, we report an experimental observation of intriguing two-dimensional superconductivity with a \\(T_c\\) up to 3.8 K at the interface between Mott insulator Ti\\(_2\\)O\\(_3\\) and polar semiconductor GaN. At the verge of superconductivity, we also observe a striking quantum metallic-like state, demonstrating that it is a precursor to the two-dimensional superconductivity as the temperature is decreased. Our work is the first time finding this intriguing superconducting state at the heterointerface, which not only brings a new broad of perspective on the emergent quantum phenomena at the heterointerfaces but also sheds new light on exploiting the novel heterointerface superconductivity with high-\\(T_c\\) via heterostructure engineering.