Revealing physical origin of electronic phase separation in complex oxides
Manganites exhibit various nonlinear responses to external stimuli, which makes them potentially useful materials for electronic devices. While nonlinear responses in complex oxides have been correlated to large-scale electronic phase separation (EPS), the physical origin of EPS has for a long time remained puzzling. The group of Jian Shen (Fudan University, China) has provided the first experimental evidence that the disorder induced by chemical doping is a prerequisite for EPS, thus verifying the theoretical predicition.
This result has been directly obtained by comparative MFM measuerments on chemically ordered manganite film vs. the chemically disordered one, utilizing an attoAFM I with attoMFM upgrade in an attoDRY1000 cryostat. Their finding opens the path to focused design of complex oxides with desired properties for applications, especially those exhibiting colossal magnetoresistance.
T. Miao et al., PNAS 117, 7090 (2020)
Anisotropic formation of exciton magnetic polarons in colloidal quantum dot
Colloidal nanocrystal quantum dots are - due to their reproducible and scalable fabrication process - promising candidates for many industrial applications like solar cells, LEDs and displays. Doping semiconducting colloidal nanocrystals with magnetic ions can lead to extraordinary effects, such as light-induced magnetization - aka exciton magnetic polaron (EMP). The group of Gerd Bacher (University of Duisburg-Essen, Germany) carried out temperature- and magnetic-field-dependent photoluminescence measurements on single colloidal Mn2+:CdSe/CdS quantum dots, thus shedding light on the fundamental processes that lead to EMP formation. The measurements were realized with attoCFM I in attoDRY1000 with 3D magnetic field. These findings open a new path for controlling the orientation of light-induced magnetism.
S. Lorenz et al., Nano Lett. 20, 1896 (2020)
Spin-Flip Phase Transitions in Multi-Layered CrI3
Newly discovered magnetic 2D materials, such as CrI3, are among the most interesting materials in nowadays research. While ferromagnetic in bulk, thin multilayers of CrI3 can be switched between ferro- and antiferromagnetic layer stacking with electric & magnetic fields, or by applied pressure. Using an unique magneto-Raman measurement capability based on attoDRY1000 and LT-APO objective, the group of Angela Hight Walker (NIST, USA) identified the transition between the antiferromagnetic and ferromagnetic phases as a function of magnetic field and temperature by tracking the lattice vibrations (phonon modes) of CrI3. Their findings highlight the sensitivity of Raman modes to magnetic order and spin flips of single layers. The study establishes magneto-Raman spectroscopy as a valuable tool to investigate magnetic phase transitions in 2D van der Waals magnets.
A. McCreary et al., Nature Commun. 11, 3879 (2020)
Single photon sources on the way to QIP
Single-photon sources will be a fundamental building block for future quantum information devices. For advanced implementations, the photon sources must emit simultaneously high efficiency and indistinguishability photons. On the way towards an optimal solid-state based single-photon source, the group of Chaoyang Lu and Jian-Wei Pan at the University of Science and Technology of China (Shanghai, CN) presented a background-free method (two-color excitation) for generating spectrally isolated indistinguishable photons  and polarized single photons from elliptical micro-pillars. The optical measurements were performed using an attoCFM I cooled by a closed cycle attoDRY2100 cryostat. With their measurement method they demonstrated a state-of-the-art polarized single-photon efficiency of up to 60% and an indistinguishability of up to 0.975 for the micro pillar device , which allowed them to perform the first 20 photon experiment leading toward quantum supremacy .
Single-photon Source at Telecom Wavelength for Quantum Computation
One of the most promising approaches towards devices that could act as a building block for quantum computing and quantum information technology are quantum dot based single photon sources. Some of the standing technical challenges are coupling efficiencies, lossy transmission of quantum states, and the integration of other photonic devices such as electro-optic modulators.
The group of Edo Waks at the University of Maryland (Maryland, USA) tackled these demands by developing an alignment-free fiber-coupled single photon source emitting at the telecom wavelength.
The heart of the device is a nanobeam with an embedded quantum dot attached to a tapered fiber. The photons emitted from the quantum dot are guided to the fiber, from which it can be transferred to other optical device. The characterization required a home-made all-fiber photoluminescence setup that was cooled to 4 K using the closed cycle attoDRY1000 cryostat. The observed single-photon emission was detected with a brightness of 1.5 % and a purity of 86 %. With these results the developed device is a promising candidate for quantum computing as it offers the required usability and performance.
Chang-Min Lee et al.; Appl. Phys. Lett. 114, 171101 (2019)
Fine-scale Stripey Morphology of an Iron Pnictide - New Findings in Material Science
Iron-based superconducting pnictides feature relatively high transition temperature and a co-existence of the superconducting state with antiferromagnetic ordering. This remarkable combination brings these materials into the focus of research. The group of Prof. Susannah Speller at the Materials Department of the University of Oxford (Oxford, UK) used an attoAFM I cooled by a closed cycle attoDRY1000 for magnetic force measurements at about 4.6 K to investigate the local electronic structure and chemistry of RbxFe2-ySe2 crystals.
The group showed a fine-scale stripey morphology of the superconducting phase which - combined with previous findings - paves the way to understand the intriguing electronic and magnetic properties of these compounds.
P Dudin et al.; Supercond. Sci. Technol. 32, 044005 (2019)
A new way to modulate exciton-complex emissions of TMDs
A new type of atomically layered transition-metal dichalcogenides (TMD) was developed by Mr. Taishen Li and co-workers from the University of Science and Technology of China (Hefei, China): a triangular inkslab-like WSe2 homojunction with a monolayer in the inner surrounded by a multilayer frame.Optical and scanning photocurrent microscopy (SPCM) measurements performed with the attoCFM I, cooled by a closed cycle attoDRY1000 to cryogenic temperatures, shows a clear redshift of the photoluminescence peaks from the center to the edge region of the inner monolayer, reflecting a high charge density gradient. In addition, a significant rectifying behavior and photovoltaic response across the homojunction is observed. All in all, the results lead to efficient modulation of the exciton-complex emissions of TMDs.
T. Li, et al., ACS Nano 12 (5), pp 4959–4967 (2018)
Measurements of field-driven transformation of a domain pattern
The group of Erik Folven at the Norwegian University of Science and Technology (Trondheim, Norway) used an attoAFM I for MFM measurements with a closed cycle attoDRY1000 to demonstrate how topological defects may be invoked to understand magnetic domain state transitions. The atomically sharp and magnetized tip of the microscope is scanned across the thin film surface to pick up the out-of plane stray fields from the sample and thus is sensitive primarily to spin textures such as domain walls and defects. The MFM measurements taken at 5K help to understand and describe micromagnetic domain state transitions and to assess their stability in remanence. This insight may open for new approaches to control the switching properties of micro- and nanomagnets.
S. D. Sloetjes, et al., Appl. Phys. Lett. 112, 042401 (2018)
Coupling single defects to a nanowire
Using an attoCFM I cooled by an attoDRY1000, the group of Edo Waks at the University of Maryland (Maryland, USA) succeeded to couple quantum emitters in a tungsten diselenide (WSe²) monolayer self-aligned to the surface plasmon mode of a silver nanowire. The achieved lower bound coupling efficiency was measured to be 26% ± 11% in average from the emitter into the plasmonic mode of the silver nanowire. The presented technique is versatile to construct coupled systems consisting of diverse plasmonic structures and single-defect emitters in a range of two-dimensional semiconductors. Such a coupled system could be used for applications such as ultra-fast single-photon sources, which paves a way toward super-compact plasmonic circuits.
T. Cai, et al., Nano Lett. 17, 6564 (2017)
Quasi-2D Magnon identified via Magneto-Raman Spectroscopy
Due to myriad of interesting electronic, mechanical and optical properties, van der Waals materials have been extensively studied in recent years. Exploring their magnetism has been neglected, mainly because of scarcity of long-range magnetic order in 2D materials. Yet, when it exists, like in FePS³, it poses a huge technological potential, particularly since magnetic properties of 2D materials are easily tuneable. The group of Angela Hight Walker at NIST (Gaithersburg, Maryland, USA) developed and used a state-of-the-art cryogenic Raman system cooled by an attoDRY1000 to investigate FePS³ in an antiferromagnetic ordering which leads to a folding of the Brillourin zone and thus to a new modes appearing below the Néel temperature TN. With their temperature and magnetic-field dependent Raman spectra, the group established that one of the appearing modes can only be explained as a magnon and not with a phonon, contrary to previous assumptions. The magnon frequency was detected at 3.7 THz which is an order of magnitude faster than in the previously studied MnPS3. To the best knowledge, this is the first verification of a quasi-2D magnon in a layered material by magneto-Raman spectroscopy.
A. McCreary et al., Phys. Rev. B 101, 064416 (2020)Press release
Scalable Architecture for Multi-Photon Boson Sampling
Research groups led by Jian-Wei Pan & Chao-Yang Lu in China and Sven Höfling in Germany & UK have successfully demonstrated the first quantum simulator based on single photons that beats early classical computers. In Nature Photonics, they report on “High-efficiency multiphoton boson sampling“, implementing 3-, 4-, and 5-boson-sampling with rates which are more than 24,000 times faster than all previous experiments, and 10-100 times faster than the first electronic computer (ENIAC) and transistorized computer (TRADIC) in human history. Their work, which was carefully prepared and accompanied by their 3 previous papers published in PRL (see below), kick starts a new era of photonic quantum technologies-going beyond proof-of-principle demonstrations and building a quantum machine to actually race against different generations of classical computers. In recognition of their achievements in quantum teleportation research, the very active and highly respected Chinese group recently also won the 2015 Physics World Breakthrough of the Year award and the 2015 State Nature Science First Class Award in China. In addition, Chao-Yang Lu was portrayed by Nature last summer as one of the “Science stars of China”. For their quantum dot experiments, his group uses three attoDRY cryostats equipped with attocube positioners, scanners and cryogenic objectives. Visit the group’s homepage for more information on their experiment.
Cryogen-free confocal measurements on a single quantum dot
The data to the left show photon anti-bunching experiments performed on a single quantum dot. The optical insert was cooled down by a closed cycle attoDRY1000 cryostat. Without any special effort the customer observed that the dot luminescence intensity remains constant within 14% over 10 hours.
(The data was generously provided by Benito Alén Millán, Molecular Beam Epitaxy group at the Instituto de Microelectrónica de Madrid, Spain)
Scanning probe microscopy in an ultra-low vibration closed-cycle cryostat
The attoDRY1000 is a cryogen-free cooling system setting new performance benchmarks. The attoDRY1000 was specifically designed to provide an ultra-low vibration measurement platform for cryogenic scanning probe experiments without the need for liquid helium.
The standard closed-cycle system enables vibration-sensitive experiments in a temperature range from 4 K to 300 K. The optionally available microscope inserts are cooled by a controlled exchange gas atmosphere. Superconducting magnets up to 9 T are available as an option. Due to a proprietary design, mechanical vibrations created by the pulse-tube coldhead are decoupled from the measurement platform.
When measured with the attoAFM I, vibration amplitudes of less than 0.15 nm RMS are routinely achieved (bandwidth of 200 Hz, vertical direction). Despite the mechanical decoupling between coldhead and sample platform, the cooling performance ot the attoDRY1000 is simply outstanding. Temperatures as low as 3 K and probe cooldown times as fast as 1 hour make cryogenic scanning probe experiments a delight.
For the attoDRY1000, a wide variety of scanning probe microscopy inserts is available, ranging from confocal (CFM) to magnetic force microscopy (MFM).
F.P. Quacquarelli et al., arXiv:1404.2046v1
MFM imaging of a Skyrmion lattice
In collaboration with Jan Seidel from UNSW Sydney, A. Bauer & C. Pfleiderer, TU Munich we have successfully imaged the elusive Skyrmions and their magnetic field evolution in the attoDRY1000 cryostats using the attoAFM/MFM I. See what’s possible nowadays with our sophisticated commercial instruments!