Intensive effort to tailor photophysics of lead-free perovskites is appealing in recent years. However, their combined electronic and optical property elucidations remain elusive. Here, we report spectroscopic observations of the coexistence Zhang-Rice singlet state and exotic electronic transitions in two-dimensional copper-based perovskites. Herein, several perovskites with different alkylammonium spacers are investigated to unravel their correlated electronic systems and optical responses. Namely, methylammonium, ethylammonium, phenylmethylammonium and phenethylammonium. Using temperature dependent high-resolution X-ray absorption spectroscopy, we observe distinct electronic features highlighting the impact of short spacer chains compared to long-conjugated ligands, demonstrating a pronounced 3d9 and 3d9L signature linewidth variation. Corroborated by density functional theory calculations, the transient dynamics evolution of copper-based hybrid perovskites is influenced by the strong interplay of electron-phonon interactions and geometric constrictions. This finding sheds light on tuning the electronic and optical properties of hybrid perovskites towards efficient photoactive-based devices.

We observe variation in the resistively-detected nuclear magnetic resonance (RDNMR) lineshapes in quantum Hall breakdown. The breakdown is locally occurred in a gate-defined quantum point contact (QPC) region. Of particular interest is the observation of a dispersive lineshape occured when the bulk 2D electron gas (2DEG) is set to ν b = 2 and the QPC filling factor to the vicinity of νQPC = 1, strikingly resemble the dispersive lineshape observed on a 2D quantum Hall state. This previously unobserved lineshape in a QPC points to simultaneous occurrence of two hyperfinemediated spin flip-flop processes within the QPC. Those events give rise to two different sets of nuclei polarized in the opposite direction and positioned at a separate region with different degree of electronic spin polarization.Recent advent in NMR technique through a resistive detection (RDNMR) has made it possible to study various spin physics in a 2D quantum Hall system [1][2][3][4][5][6][7], and a quasi-1D channel [8,9]. Despite the success achieved, a certain aspect related to the origin of the RDNMR lineshape variations noted experimentally in continuous wave (cw) mode is still poorly understood. One of them involved the puzzling observation of a dispersive lineshape in the quantum Hall state, a resistance dip followed by a resistance peak resonance line with increasing radio frequency [10]. It is first reported by Desrat et al [11] in the vicinity of ν b = 1 and has been confirmed in a number of follow-up papers [7,[12][13][14][15][16][17]. Similar dispersive like lineshape has been observed as well in the vicinity of ν b = 2/9[18], ν b = 2/3, ν b = 1/3 [19], and at ν b = 2 Landau level crossing [20]. A number of appealing explanations has been put forward, but none of them provides a comprehensive explanation. Part of the reason why it still is difficult to unravel its physical origin is that we do not have a mature level of understanding about manybody 2D electronic states at the first Landau level yet, let alone their coupling to the nuclear spin. Thus, it would be highly desirable to study the lineshape variations in a platform where one can avoid such complexity.In this Rapid Communication, we resort to a quasione dimensional system in a gate-defined quantum point contact (QPC) to study various possible lineshapes including the dispersive lineshape noted experimentally in cw mode. Unlike on the 2D system, the mechanism for generation and resistive detection of nuclear spin polarization is tractable, allowing conveniently a direct interpretation of the observed lineshapes.Generation and detection of nuclear spin polarization are achieved by setting the filling factor in the bulk 2DEG to ν b = 2 and ν QPC = 1 in the QPC[21-30]. Fig. 1(a)-(b) schematically displays how the nuclear polarization affects the transmission probability through the potential barrier of the QPC. For ν QPC < 1 (the down-spin channel T ↓ does not affect the transport), the up-spin channel T ↑ sees an increase(decrease) in the barrier potential in the presence of p...

layer-modulated magnetism and robust stability in air. These properties make it a promising candidate in various fields like electronics, [1][2][3][4][5] optoelectronics, [6][7][8][9][10][11][12][13] spintronics, [14] catalysis, [15] micro-electromechanics, [16] and sensing. [6,17,18] Monolayer or few-layer PtSe 2 can be synthesized by different methods, such as direct selenization of Pt films at a low temperature (≤400 °C), [3,4,6,8,19] which makes it scalable and compatible with current silicon chip fabrication technology, molecular beam epitaxy (MBE), [16,20,21] chemical vapor deposition (CVD), [5,22] and chemical vapor transport (CVT). [1,23] While PtSe 2 is a semimetal in bulk, [23] it becomes a semiconductor when thinned down to a few layers, due to the quantum confinement effect. [3] Its electronic structure has been studied by angle-resolved photoemission spectroscopy (ARPES), which reveals the semiconducting property of monolayer PtSe 2 with the top of its valence band located at 1.2 eV below the Fermi level. [17,20] Complemented by density functional theory (DFT) calculations under the localizeddensity approximation (DFT-LDA), monolayer PtSe 2 is determined to be an indirect-gap semiconductor (≈1.2 eV). [17] Besides the first layer, PtSe 2 remains semiconducting at the thickness of bilayer with a significantly reduced gap of 0.21 eV and becomes semimetallic from the third layer, as predicted by DFT-LDA calculations. [17,24] However, the ARPES measurement only gives the area-average information of the band structure below the Fermi level and its results are subject to the crystal size and quality. For

Gate patterning on semiconductors is routinely used to electrostatically restrict electron movement into reduced dimensions. At cryogenic temperatures, where most studies are carried out, differential thermal contraction between the patterned gate and the semiconductor often lead to an appreciable strain modulation. The impact of such modulated strain to the conductive channel buried in a semiconductor has long been recognized, but measuring its magnitude and variation is rather challenging. Here we present a way to measure that modulation in a gate-defined GaAs-based onedimensional channel by applying resistively-detected NMR (RDNMR) with in-situ electrons coupled to quadrupole nuclei. The detected strain magnitude, deduced from the quadrupole-split resonance, varies spatially on the order of 10 −4 , which is consistent with the predicted variation based on an elastic strain model. We estimate the initial lateral strain xx developed at the interface to be about 3.5 × 10 −3 .In many semiconductor-based quantum systems, electrons are manipulated by applying voltages to the surface metal gates. For example, a combination of nanoscale metal gates and GaAs based two-dimensional systems enables us to realize one-dimensional quantum channel and zero-dimensional quantum dot by depleting electrons under the gates[1]. These building blocks are integrated into many quantum devices, such as quantum computing/simulating systems based on electron spins [2][3][4]. Electron control in these systems is always accompanied by electron position change from the originally twodimensional sheet. One can expect microscopic strain distribution in such devices because surface metal gate and semiconductor system have different thermal expansion coefficients and complicated nanometer surface gates should produce a complicated strain pattern inside. Such phenomena are common for all semiconductor systems including silicon and other semiconductor groups. However, the strain variation felt by confined electrons has not received much attention up to now partly because a lack of appropriate and precise measurement tool to probe local strain in nanometer scale electron channel. Here, taking GaAs-based quantum-point-contact (QPC)[5, 6] as a prototypical example, we demonstrate that electrons flowing in the one-dimensional channel feel different strain even in the same device when the channel position is microscopically shifted by changing the gate voltage.There are a couple of methods to measure spatial strain distribution in materials. Examples include X-ray diffraction [7,8], electron microscopy [9,10], and Raman spectroscopy [11][12][13]. Although those techniques are capable of delivering a high-spatial resolution strain profile, they are only sensitive to strain magnitude larger than a factor of 10 −4 . Alternative technique such as solidstate NMR could provide an acceptable solution since it has the ability to detect ultra low-level strain variation of less than 10 −4 through nuclear quadrupolar interaction with the electric field gradient ...

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