Recent developments of imaging techniques have enabled fluorescence microscopy to investigate the localization and dynamics of intracellular substances of interest even at the single-molecule level. However, such sensitive detection is often hampered by autofluorescence arising from endogenous molecules. Those unwanted signals are generally reduced by utilizing differences in either wavelength or fluorescence lifetime; nevertheless, extraction of the signal of interest is often insufficient, particularly for in vivo imaging. Here, we describe a potential method for the selective imaging of nitrogen-vacancy centers (NVCs) in nanodiamonds. This method is based on the property of NVCs that the fluorescence intensity sensitively depends on the ground state spin configuration which can be regulated by electron spin magnetic resonance. Because the NVC fluorescence exhibits neither photobleaching nor photoblinking, this protocol allowed us to conduct long-term tracking of a single nanodiamond in both Caenorhabditis elegans and mice, with excellent imaging contrast even in the presence of strong background autofluorescence.

We present CuO 2 plane 17 O NMR measurements for Ni-substituted YBa 2 Cu 3 O 61y . The Ni moment induces an oscillatory spin density responsible for the broadening of the NMR line. In slightly overdoped y 1 compounds, this broadening scales with the Ni susceptibility. In contrast, such a scaling is not found in underdoped y 0.6 samples. We associate it with the T dependence of the antiferromagnetic staggered spin susceptibility x 0 ͑Q AF ͒ intrinsic to the CuO 2 planes. Discussion with respect to 63 Cu NMR transverse relaxation (T 2G ) and neutron scattering data shows that the AF correlation length j is T independent. [S0031-9007 (97)03937-9] PACS numbers: 74.25.Nf, 74.62.DhThe normal state of high-T c superconductors exhibits a peculiar magnetic behavior, distinct from that of a normal metal [1]. In the underdoped regime, well above T c , the static susceptibility x͑q 0͒ shows an anomalous "pseudogap" decrease with decreasing temperature T [2]. Simultaneously, antiferromagnetic (AF) correlations occur within the CuO 2 planes, as evidenced by an enhancement of the imaginary part of the susceptibility x 00 near the AF wave vector seen both in neutron scattering [3] and 63 Cu NMR longitudinal relaxation time [4]. These AF correlations might play a crucial role in the mechanism of superconductivity in these materials [5]. Thus, the AF correlation length j and both the imaginary and the real part of the staggered susceptibility at Q AF are major parameters for any coherent description of the cuprates. No clear experimental agreement on the T dependence of j and x 0 ͑q͒ is yet achieved. An integral information on x 0 ͑q͒ is available through 63 Cu transverse relaxation data ( 63 T 2G ) [6-9]. These data are usually analyzed as an increase of j at low T [10], whereas neutron experiments for x 00 suggest that j is T independent in YBa 2 Cu 3 O 61y [3]. No other technique has been used up to now to determine x 0 ͑q͒ at q fi 0.We propose here a new approach to probe x 0 ͑q͒, using magnetic impurity substitution effects in the CuO 2 planes. The impurity magnetic moment gm B ͗S Z ͘ acts as a local field H͑r͒~͗S Z ͘d͑r͒, which induces an in-plane spin polarization s͑r͒~x 0 ͑r͒͗S Z ͘. This polarization may be probed by the NMR of nuclei coupled to the planes: at r from the impurity, the NMR frequency shift dnH hf x 0 ͑r͒͗S Z ͘ is due to the hyperfine coupling H hf with the spin density. Hence, the broadening due to the shift distribution among the nuclei yields information on x 0 ͑r͒. We will show here that the use of the 17 O NMR probe allows us, for the first time, a thorough investigation of x 0 ͑r͒. This approach contrasts with the usual impurity studies of the specific properties of the magnetic defects [11] and their influence on superconductivity [12]. We find an anomalously large T variation of the 17 O linewidth for the underdoped composition. The specific geometry of the 17 O nuclei within the planes allows us through extended numerical simulations to demonstrate that the 17 O linewidth probes the amplitude of x 0 ...

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The rotation of an object cannot be fully tracked without understanding a set of three angles, namely, roll, pitch, and yaw. Tracking these angles as a three-degrees-of-freedom (3-DoF) rotation is a fundamental measurement, facilitating, for example, attitude control of a ship, image stabilization to reduce camera shake, and self-driving cars. Until now, however, there has been no method to track 3-DoF rotation to measure nanometer-scale dynamics in biomolecules and live cells. Here we show that 3-DoF rotation of biomolecules can be visualized via nitrogen-vacancy centers in a fluorescent nanodiamond using a tomographic vector magnetometry technique. We demonstrate application of the method to three different types of biological systems. First, we tracked the rotation of a single molecule of the motor protein F1-ATPase by attaching a nanodiamond to the γ-subunit. We visualized the 3-step rotation of the motor in 3D space and, moreover, a delay of ATP binding or ADP release step in the catalytic reaction. Second, we attached a nanodiamond to a membrane protein in live cells to report on cellular membrane dynamics, showing that 3D rotational motion of the membrane protein correlates with intracellular cytoskeletal density. Last, we used the method to track nonrandom motions in the intestine of Caenorhabditis elegans. Collectively, our findings show that the method can record nanoscale 3-DoF rotation in vitro, in cells, and even in vivo. 3-DoF rotation tracking introduces a new perspective on microscopic biological samples, revealing in greater detail the functional mechanisms due to nanoscale dynamics in molecules and cells.

We have performed 13 C NMR measurements on the three phases of A 1 C 60 ͑A K, Rb, Cs͒ and alkali NMR in Cs 1 C 60 ( 133 Cs) and Rb 1 C 60 ( 87 Rb). We show that, for Rb 1 C 60 and Cs 1 C 60 , strong antiferromagnetic (AF) fluctuations persist up to room temperature, suggesting a one-dimensional character. However, K 1 C 60 behaves as an ordinary three-dimensional metal. NMR also reveals a magnetic transition at about 25 K in the Rb and Cs polymers. Comparison of the 133 Cs and 13 C spectra supports the occurrence of a spin-flop AF phase. Simulations of the 133 Cs spectrum due to a distribution of dipolar fields are consistent with moments m Ӎ 0.5m B ordered in AF chains.[S0031-9007(96)00161-5] PACS numbers: 76.60. Es, 61.48.+c, 75.50.Ee It is by now well established that the A 1 C 60 compounds display an orthorhombic ͑o͒-phase below room temperature, where the C 60 balls form polymerized chains in the a direction [1,2]. Yet the consequences of this strongly one-dimensional (1D) structure on the symmetry of the electronic properties of these systems are still debated. Shortly after the synthesis of this new phase, Chauvet et al. argued [1], interpreting their ESR measurements, that ͑o͒-Rb 1 C 60 is a quasi-1D conductor, where spin or charge density wave (SDW or CDW) instabilities lead to an insulating ground state. A transition at about 50 K has actually been confirmed for Rb 1 C 60 and Cs 1 C 60 through various experiments [ESR, conductivity [3], and muon spin resonance (mSR) [4-6]]; such a transition is not detected in K 1 C 60 either by ESR or by conductivity despite the structural similarity [3], although the eventual occurrence of a CDW state is controversial [3,7]. The exact nature of the transition in Rb 1 C 60 and Cs 1 C 60 is still unclear: mSR seems to favor a highly disordered magnetic state. On the other hand, Erwin, Krishna, and Mele claim that from band structure calculations [8] in the polymer phase the electronic density at the bonding sites between C 60 balls is small, and therefore the transfer integral along the chain is too weak to display a 1D character. As a consequence, the electronic properties should remain three dimensional (3D).In this context, local magnetic probe studies are highly desirable. We present here a thorough study of the various nuclear spins, which allows us to extract a 1D antiferromagnetic (AF) component of the spin fluctuations in the Rb and Cs polymers. In Cs 1 C 60 , the comparison between the 133 Cs and 13 C low T spectra leads us to conclude that the broadening is not due to static hyperfine fields and is better explained by dipolar fields in a spinflop AF phase.The 13 C relaxation data shown in Fig. 1 demonstrate immediately that T 1 behaves quite differently in Rb 1 C 60 and Cs 1 C 60 , on one hand, and K 1 C 60 , on the other hand. In K 1 C 60 , both T 1 T 300 sec K and the spin susceptibility [3] are T independent, which is the usual situation for an ordinary 3D metal. On the contrary, ͑T 1 T͒ 21 increases with decreasing T 1 as T 1 is nearly T independent in ...

139 La nuclear quadrupole resonance measurements in lightly doped La2Cu 1−x LixO4 have been performed to reveal the dependence of the magnetic properties of the antiferromagnetic CuO2 planes on the character of the doped holes and their interactions with the dopant. A detailed study shows that the magnetic properties are remarkably insensitive to the character of the dopant impurity. This indicates that the added holes form previously unrecognized collective structures. PACS numbers: 75.30. Kz, 76.60.Jx, 74.72.Dn, 76.60.Gv Full understanding of the character of holes added to cuprate planes and their interactions with the twodimensional lattice of Cu spins remains a crucial and unsolved problem in the high temperature superconductors. While the detailed mechanism is poorly understood, the rapid suppression of the antiferromagnetic (AF) ordering temperature T N by doping is clearly related to the disruptive effects of mobile holes: < ∼ 3% added holes whether from Sr substitution, addition of interstitial oxygen or inplane substitution of Li for Cu [1] suppresses T N to zero, yet ∼ 30% isovalent substitution of Zn or Mg for Cu is required [2] to produce the same effect. Li and Sr-doped holes have very different mobilities. For x or y ≈ 0.025, the room temperature resistivity ρ of La 2 Cu 1−x Li x O 4 exceeds that of La 2−y Sr y CuO 4 by over an order of magnitude [1,3,4]; more strikingly, for Sr-doping dρ/dT > 0 for T > ∼ 100 K, in contrast to the negative slope found in Li-doped material for all x and T .It is well recognized that the 2D cuprates are inclined toward microscopic charge inhomogeneity [5][6][7]. Evidence for such an effect in lightly doped La 2−y Sr y CuO 4 was obtained from a scaling analysis of the doping y and temperature T dependence of the static susceptibility χ(y, T ) [8] which indicated that the magnetic correlation length is limited to the dimensions of AF domains (finitesize scaling) formed by microsegregation of doped holes into hole-rich domain walls surrounding hole-free, AF domains. Interpretations involving charge-stripes have also been proposed [9]. Castro Neto and Hone [10] have examined the influence of doping on the long wavelength properties of a 2D antiferromagnet in a model in which charged stripes cause the exchange coupling J to become anisotropic; this model reproduces the relationship between M 0 s (M s is the sublattice magnetization; M 0 s is that obtained by extrapolation of data for T > 30 K to T = 0) and T N as the two are suppressed by Sr-doping in La 2−y Sr y CuO 4 [11]. However, using a similar model, van Duin and Zaanen [12] find that T N is suppressed much more rapidly than M 0 s with increasing anisotropy (doping).We have used 139 La nuclear quadrupole resonance (NQR) measurements to microscopically examine the effects of doped holes on the AF spin correlations in La 2 Cu 1−x Li x O 4 (0.019 < x < 0.025). We find that the magnetic behavior of lanthanum cuprate is remarkably insensitive to the detailed nature of the dopant, in spite of the differing charge tran...

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139 La nuclear magnetic resonance studies reveal markedly different magnetic properties of the two sites created by the charged domain wall formation in La 5/3 Sr 1/3 NiO4. NMR is slow compared to neutron scattering; we observe a 30 K suppression in magnetic ordering temperature indicating glassy behavior. Applied magnetic field reorients the in-plane ordered moments with respect to the lattice, but the relative orientation of the spins amongst themselves is stiff and broadly distributed. PACS 74.72.Bk, 75.30.Ds, 75.40.Gb Since the discovery of high temperature superconductivity in the cuprates, the behavior of holes added to a strongly correlated two dimensional (2D) antiferromagnet has been a subject of intense interest. One important aspect of this system is its tendency toward inhomogeneous charge distribution [1]. In particular, segregation of doped holes into periodic arrays of charged stripes separating hole-free domains has been predicted [2]. Stripe ordering has been observed in doped La 2 NiO 4 [3-6] which remains semiconducting up to very high Sr content [7]. The recent observation of similar elastic superlattice peaks in the isostructural [8,9] high-T c superconductor La 1.48 Nd 0.4 Sr 0.12 CuO 4 [10] indicates the existence of similar charge ordered structures, and suggests these structures may be relevant to cuprate superconductivity [11][12][13][14]. Similarities between these elastic superlattice peaks and the incommensurate peaks observed in inelastic neutron studies of La 2−x Sr x CuO 4 [15] have been noted [16]. Hence, these incommensurate peaks are being reconsidered as possible evidence for the presence of dynamic charged stripes in the cuprate [16].There is clear evidence for stripe formation in doped 2D AF systems [3][4][5][6], but detailed microscopic studies of their low energy dynamic and static magnetic properties are lacking. A detailed elastic neutron diffraction study of the title compound [6] has demonstrated charge ordering at T co = 240 K [6,17,18] into domain walls or "stripes." The stripes run along two equivalent diagonal directions e = (1, 1) or (1,1) in the tetragonal unit cell with dimensions a t × a t in the basal plane where a t is the is the lattice parameter corresponding to the Ni-Ni spacing. The stripe period perpendicular to the stripes is 3a t / √ 2. At T NS so = 190 K, spin superlattice peaks appear indicating ordering of the spins between the stripes. Three temperature regions were evident, the highest between T NS so and T co exhibited elastic charge order peaks with weaker intensity and significantly reduced correlation lengths compared to lower temperatures. The authors proposed the existence of a "stripe glass" in this temperature regime, but were unable to study the very important issue of orientational order due to the dominant affect of short stripes. Below T NS so the charge stripe order was found to improve.In this Letter we report a single crystal 139 La NMR study of the two magnetically distinct sites observed below T co , the first located in the d...