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  1. Free, publicly-accessible full text available July 4, 2024
  2. Recently, there has been considerable interest in x-ray and gamma ray detectors with large volume and high energy resolution that operate at room temperature. To improve detector energy resolution, the carrier mobility-lifetime product needs to be increased, and the electronic trap state concentration needs to be minimized. Defect concentrations in the part per billion range can alter the charge transport and carrier recombination lifetime. In this work, thermally stimulated current spectroscopy measurements were systematically carried out in bulk halide perovskite single crystals of CsPbBr3 over a temperature range of 80–320 K. The origins and trap parameters of CsPbBr3 crystals from the solution growth and melt growth procedures were determined and compared. Trap concentrations were ranged from 1 × 1011 to 1 × 1016 cm−3. Appreciable detector performance was observed for CsPbBr3 crystals with trap concentrations less than 1 × 1014 cm−3. The comparison of spectral responses of crystal samples grown using two different methods shows that, after purification, solution-grown crystals are comparable to melt-grown crystals in terms of low defect concentration and improved detector performance. For an improved mobility-lifetime product and enhanced spectral response to high energy radiation from fissile materials, trap states in either type of a crystal ingot must be reduced closer to 1011 cm−3.

    Free, publicly-accessible full text available March 29, 2024
  3. Abstract

    The quantum anomalous Hall (QAH) effect is characterized by a dissipationless chiral edge state with a quantized Hall resistance at zero magnetic field. Manipulating the QAH state is of great importance in both the understanding of topological quantum physics and the implementation of dissipationless electronics. Here, the QAH effect is realized in the magnetic topological insulator Cr‐doped (Bi,Sb)2Te3(CBST) grown on an uncompensated antiferromagnetic insulator Al‐doped Cr2O3. Through polarized neutron reflectometry (PNR), a strong exchange coupling is found between CBST and Al‐Cr2O3surface spins fixing interfacial magnetic moments perpendicular to the film plane. The interfacial coupling results in an exchange‐biased QAH effect. This study further demonstrates that the magnitude and sign of the exchange bias can be effectively controlled using a field training process to set the magnetization of the Al‐Cr2O3layer. It demonstrates the use of the exchange bias effect to effectively manipulate the QAH state, opening new possibilities in QAH‐based spintronics.

    Free, publicly-accessible full text available May 19, 2024
  4. Abstract

    Spintronics applications of thin‐film magnets require control and design of specific magnetic properties. Exchange bias, originating from the pinning of spins in a ferromagnet by these of an antiferromagnet, is a part of the highly important elements for spintronics applications. Here, an exchange bias of ≈90 mT in a van der Waals ferromagnet encapsulated by two antiferromagnets at 5 K, the value of which is highly tunable by the field coolings, is reported. The non‐antisymmetric dependence of exchange bias on field cooling is explained through considering an uncompensated interfacial magnetic layer of an antiferromagnet with a noncollinear spin texture, and a weak antiferromagnetic order in the oxidized layer, at two ferromagnet/antiferromagnet interfaces. This work opens up new routes toward designing and controlling 2D spintronic devices made of atomically thin van der Waals magnets.

  5. Abstract

    Spectroscopic‐grade single crystal detectors can register the energies of individual X‐ray interactions enabling photon‐counting systems with superior resolution over traditional photoconductive X‐ray detection systems. Current technical challenges have limited the preparation of perovskite semiconductors for energy‐discrimination X‐ray photon‐counting detection. Here, this work reports the deployment of a spectroscopic‐grade CsPbBr3Schottky detector under reverse bias for continuum hard X‐ray detection in both the photocurrent and spectroscopic schemes. High surface barriers of1 eV are formed by depositing solid bismuth and gold contacts. The spectroscopic response under a hard X‐ray source is assessed in resolving the characteristic X‐ray peak. The methodology in enhancing X‐ray sensitivity by controlling the X‐ray energies and flux, and voltage, is described. The X‐ray sensitivity varies between a few tens to over 8000 μC Gyair−1cm−2. The detectable dose rate of the CsPbBr3detectors is as low as 0.02 nGyairs−1in the energy discrimination configuration. Finally, the unbiased CsPbBr3device forms a spontaneous contact potential difference of about 0.7 V enabling high quality of the CsPbBr3single crystals to operate in “passive” self‐powered X‐ray detection mode and the X‐ray sensitivity is estimated as 14 μC Gyair−1cm−2. The great potential of spectroscopic‐grade CsPbBr3devices for X‐ray photon‐counting systems is anticipated in this work.

  6. Quantum anomalous Hall effect has been observed in magnetically doped topological insulators. However, full quantization, up until now, is limited within the sub–1 K temperature regime, although the material’s magnetic ordering temperature can go beyond 100 K. Here, we study the temperature limiting factors of the effect in Cr-doped (BiSb) 2 Te 3 systems using both transport and magneto-optical methods. By deliberate control of the thin-film thickness and doping profile, we revealed that the low occurring temperature of quantum anomalous Hall effect in current material system is a combined result of weak ferromagnetism and trivial band involvement. Our findings may provide important insights into the search for high-temperature quantum anomalous Hall insulator and other topologically related phenomena.