Visualization of superparamagnetic dynamics in magnetic topological insulators

Lachman, Ella; Young, Andrea; Richardella, Anthony; Cuppens, J.; Naren, H. R.; Anahory, Yonathan; Meltzer, Alexander Y.; Kandala, Abhinav; Kempinger, Susan; Myasoedov, Y.; Huber, M. E.; Samarth, N.; Zeldov, E.

doi:10.1126/sciadv.1500740

Cited by 155 publications

(168 citation statements)

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“…Other systems of interest are topologically protected surface states, edge states in quantum spin and anomalous quantum Hall systems, and surface states in Weyl semimetals. By choosing appropriate superconducting materials 22,23,33 it should be possible to extend the operating temperature range of the tSOT from tens of mK to tens of K (Fig. S1d) thus allowing investigation of a wide range of quantum systems.…”

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confidence: 99%

Nanoscale thermal imaging of dissipation in quantum systems

Halbertal

Cuppens

Shalom

et al. 2016

Nature

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Energy dissipation is a fundamental process governing the dynamics of physical, chemical, and biological systems. It is also one of the main characteristics distinguishing quantum and classical phenomena. In condensed matter physics, in particular, scattering mechanisms, loss of quantum information, or breakdown of topological protection are deeply rooted in the intricate details of how and where the dissipation occurs. Despite its vital importance the microscopic behavior of a system is usually not formulated in terms of dissipation because the latter is not a readily measureable quantity on the microscale. Although nanoscale thermometry is gaining much recent interest [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] , the existing thermal imaging methods lack the necessary sensitivity and are unsuitable for low temperature operation required for study of quantum systems. Here we report a superconducting quantum interference nano-thermometer device with sub 50 nm diameter that resides at the apex of a sharp pipette and provides scanning cryogenic thermal sensing with four orders of magnitude improved thermal sensitivity of below 1 µK/Hz 1/2 . The non-contact non-invasive thermometry allows thermal imaging of very low nanoscale energy dissipation down to the fundamental Landauer limit [16][17][18] of 40 fW for continuous readout of a single qubit at 1 GHz at 4.2 K. These advances enable observation of dissipation due to single electron charging of individual quantum dots in carbon nanotubes and reveal a novel dissipation mechanism due to resonant localized states in hBN encapsulated graphene, opening the door to direct imaging of nanoscale dissipation processes in quantum matter. 2 Investigation of energy dissipation on the nanoscale is of major fundamental interest for a wide range of disciplines from biological processes, through chemical reactions, to energy-efficient computing [1][2][3][4][5] . Study of dissipation mechanisms in quantum systems is of particular importance because dissipation demolishes quantum information. In order to preserve a quantum state the dissipation has to be extremely weak and hence hard to measure. As a figure of merit for detection of low power dissipation in quantum systems 16 we consider an ideal qubit operating at a typical readout frequency of 1 GHz. Landauer's principle states the lowest bound on energy dissipation in an irreversible qubit operation to be 0 = B ln 2, where B is Boltzmann's constant and is the temperature 17,18 . At = 4.2 K, 0 = 410 -23 J, several orders of magnitude below 10 -19 J of dissipation per logical operation in present day superconducting electronics and 10 -15 J in CMOS devices 19,20 . Hence the power dissipated by an ideal qubit operating at a readout rate of = 1 GHz will be as low as = 0 = 40.2 fW. The resulting temperature increase of the qubit will depend on its size and the thermal properties of the substrate. For example, a 120 × 120 nm 2 device on a 1 µm thick SiO 2 /Si substrate dissipating 40 fW will heat up by about 3 µK (Fig. 1). Suc...

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confidence: 99%

Nanoscale thermal imaging of dissipation in quantum systems

Halbertal

Cuppens

Shalom

et al. 2016

Nature

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“…In contrast to conventional two-terminal/two-junction SQUIDs that display optimal sensitivity when flux biased to about a quarter of the flux quantum, the additional terminals and junctions allow optimal sensitivity at arbitrary applied flux, thus eliminating the magnetic field "blind spots". We demonstrate spin sensitivity of 5 to 8 µ B /Hz 1/2 over a continuous field range of 0 to 0.5 T, with promising applications for nanoscale scanning magnetic imaging.KEYWORDS: superconducting quantum interference device, SQUID on tip, nanoscale magnetic imaging, current-phase relations 2 In recent years, there has been a growing effort to develop and apply nanoscale magnetic imaging tools in order to address the rapidly evolving fields of nanomagnetism and spintronics.These include magnetic force microscopy (MFM) 1,2 , magnetic resonance force microscopy (MRFM) [3][4][5] , nitrogen vacancy (NV) centers sensors [6][7][8][9] , scanning Hall probe microscopy (SHPM) 10-12 , x-ray magnetic microscopy (XRM) 13 , and micro-or nano-superconducting quantum interference device (SQUID) [14][15][16][17][18][19][20] based scanning microscopy (SSM) [21][22][23][24][25][26][27][28][29][30][31][32] . Scanning micro-and nanoscale SQUIDs are of particular interest for magnetic imaging due to their high sensitivity and large bandwidth 15,19 .…”

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Electrically Tunable Multiterminal SQUID-on-Tip

et al. 2016

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We present a new nanoscale superconducting quantum interference device (SQUID) whose interference pattern can be shifted electrically in-situ. The device consists of a nanoscale fourterminal/four-junction SQUID fabricated at the apex of a sharp pipette using a self-aligned threestep deposition of Pb. In contrast to conventional two-terminal/two-junction SQUIDs that display optimal sensitivity when flux biased to about a quarter of the flux quantum, the additional terminals and junctions allow optimal sensitivity at arbitrary applied flux, thus eliminating the magnetic field "blind spots". We demonstrate spin sensitivity of 5 to 8 µ B /Hz 1/2 over a continuous field range of 0 to 0.5 T, with promising applications for nanoscale scanning magnetic imaging.KEYWORDS: superconducting quantum interference device, SQUID on tip, nanoscale magnetic imaging, current-phase relations 2 In recent years, there has been a growing effort to develop and apply nanoscale magnetic imaging tools in order to address the rapidly evolving fields of nanomagnetism and spintronics.These include magnetic force microscopy (MFM) 1,2 , magnetic resonance force microscopy (MRFM) [3][4][5] , nitrogen vacancy (NV) centers sensors [6][7][8][9] , scanning Hall probe microscopy (SHPM) 10-12 , x-ray magnetic microscopy (XRM) 13 , and micro-or nano-superconducting quantum interference device (SQUID) [14][15][16][17][18][19][20] based scanning microscopy (SSM) [21][22][23][24][25][26][27][28][29][30][31][32] . Scanning micro-and nanoscale SQUIDs are of particular interest for magnetic imaging due to their high sensitivity and large bandwidth 15,19 . The two main technological approaches to the fabrication of scanning SQUIDs are based on planar lithographic methods 21,26,[33][34][35][36] and on self-aligned SQUIDon-tip (SOT) deposition 22,24,37 .In the planar SQUID architecture, spatial resolution is limited but pickup and modulation coils can be integrated to allow operation of the SQUID at optimal flux bias conditions using a fluxlocked loop (FLL) feedback mechanism 15,18,19,21,33,38,39 . Because the magnetic field of the sample is not coupled to the SQUID loop directly, but rather through a pickup coil, integration of a modulation coil or an integrated current-carrying element 15,19,21,33,38,39 allows the total flux in the SQUID loop to be maintained at its optimal bias while the magnetic field of the sample is varied independently.SOTs, in contrast, have better spatial resolution due to their small size and close proximity to the sample, attain higher spin sensitivity, and can operate at high magnetic fields 24 . The nanoscale proximity of the SOT to the sample surface, which is its key advantage, dictates however that the flux in the SQUID loop is directly coupled to the local field of the sample and therefore cannot be modified independently. As a result, the FLL concept cannot be implemented in direct nanoscale magnetic imaging. This poses a significant drawback, since the high sensitivity of the SOT is achieved only at specific field va...

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“…2,13,16 Indeed, a number of studies using global magnetization measurements 14,17,18 and magnetic force microscopy 19,20 have observed FM-like response in magnetically doped TI thin films. Surprisingly, however, recent scanning SQUID magnetic imaging 21 and transport studies, 22,23 as well as analysis of Kerr microscopy imaging, 24 have suggested the presence of a superparamagnetic (SPM) state in Cr-doped (Bi, Sb) 2 Te 3 films in which instead of a long-range FM order the magnetism is comprised of single-domain magnetic islands. These islands are of characteristic size of few tens of nanometers and are only weakly coupled to each other.…”

Section: Introductionmentioning

confidence: 99%

“…These islands are of characteristic size of few tens of nanometers and are only weakly coupled to each other. 21 The possible presence of a SPM order has important implications for the properties of the QAH state. The first key consideration is that if the QAH state can indeed be induced by a SPM order, such coexistence can be present only at temperatures well below the SPM blocking temperature, T≪T B , since at higher temperatures the QAH state will be destroyed by thermally activated magnetization reversals of the SPM islands.…”

Section: Introductionmentioning

confidence: 99%

Observation of superparamagnetism in coexistence with quantum anomalous Hall C = ±1 and C = 0 Chern states

et al. 2017

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Simultaneous transport and scanning nanoSQUID-on-tip magnetic imaging studies in Cr-(Bi,Sb) 2 Te 3 modulation-doped films reveal the presence of superparamagnetic order within the quantum anomalous Hall regime. In contrast to the expectation that a longrange ferromagnetic order is required for establishing the quantum anomalous Hall state, superparamagnetic dynamics of weakly interacting nanoscale magnetic islands is observed both in the plateau transition regions, as well as within the fully quantized C = ±1 Chern plateaus. Modulation doping of the topological insulator films is found to give rise to significantly larger superparamagnetic islands as compared to uniform magnetic doping, evidently leading to enhanced robustness of the quantum anomalous Hall effect. Nonetheless, even in this more robust quantum state, attaining full quantization of transport coefficients requires magnetic alignment of at least 95% of the superparamagnetic islands. The superparamagnetic order is also found within the incipient C = 0 zero Hall plateau, which may host an axion state if the top and bottom magnetic layers are magnetized in opposite directions. In this regime, however, a significantly lower level of island alignment is found in our samples, hindering the formation of the axion state. Comprehension and control of superparamagnetic dynamics is thus a key factor in apprehending the fragility of the quantum anomalous Hall state and in enhancing the endurance of the different quantized states to higher temperatures for utilization of robust topological protection in novel devices. 1-3 In the QH state the TRSB is induced by high magnetic field applied perpendicular to a high-mobility 2D electron gas. The QAH state, in contrast, can be formed in thin films of topological insulators (TI) even in the absence of magnetic field.3-10 In this case the TRSB is induced by magnetic order attained by doping the TIs with transition metal elements like Cr, V, or Mn,

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Visualization of superparamagnetic dynamics in magnetic topological insulators

Abstract: The ferromagnetic state of topological insulators showing quantum anomalous Hall effect is surprisingly superparamagnetic.

Cited by 155 publications

References 32 publications

Nanoscale thermal imaging of dissipation in quantum systems

Nanoscale thermal imaging of dissipation in quantum systems

Electrically Tunable Multiterminal SQUID-on-Tip

Observation of superparamagnetism in coexistence with quantum anomalous Hall C = ±1 and C = 0 Chern states

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